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Bureau of Mines Information Circular/1986 



Chromium-Chromite: Bureau of Mines 
Assessment and Research 

Proceedings of Bureau of Mines Briefing Held 
at Oregon State University, Corvallis, OR, 
June 4-5, 1985 

Compiled by Charles B. Daellenbach 




UNITED STATES DEPARTMENT OF THE INTERIOR 



i (fyjit M&* • &*"*' 



Information Circular/ 9087 



Chromium-Chromite: Bureau of Mines 
Assessment and Research 

Proceedings of Bureau of Mines Briefing Held 
at Oregon State University, Corvallis, OR, 
June 4-5, 1985 

Compiled by Charles B. Daellenbach 




■a 



UNITED STATES DEPARTMENT OF THE INTERIOR 
Donald Paul Hodel, Secretary 

BUREAU OF MINES 
Robert C. Horton, Director 






<\V< 




Library of Congress Cataloging-in-Publication Data 



Chromium-chromite. 




(Information circular / Bureau of Mines ; 9087) 




Bibliography. 




Supt. of Docs, no.: I 28.27: 9087. 




1. Chromite- United States - Congresses. 2. Chromium-Metallurgy-Congresses. I. 1 
Series: Information circular (United States. Bureau of Mines) ; 9087. 


Daellenhach, C. B. II. 


TN295.U4 [TN490.C4] 622 s [669'.734] 


86-600120 



PREFACE 



Chromium is vital to the Nation's economy and is one of its most important critical and 
strategic materials. Chromium has a wide range of uses in chemical, metallurgical, and 
refractory industries. Although the United States is the world's leading consumer of 
chromium-bearing materials, it currently has no domestic production of chromite ore. The 
mineral chromite is the sole commercial source of chromium. Today the United States 
is totally dependent on foreign sources for its primary chromium materials. 

With this background of national concern for chromium and chromite resources, the 
Bureau of Mines has had, for some time, a comprehensive program of chromium assess- 
ment and research. The objective of this 1985 Chromium-Chromite Briefing was to draw 
together the various elements of the current program and to present to industry, the public, 
and Government agencies the Bureau's multifaceted activities. Authors were drawn from 
three of the Bureau's directorates: Minerals Data Analysis, Minerals Information, and 
Minerals and Materials Research. The authors covered, through 18 presentations, a variety 
of topics including U.S. chromite and chromium trends and usage patterns; foreign and 
domestic resources; and research activities on mineral characterization and beneficiation, 
chemical and pyrometallurgical processing of chromite and chromium-bearing wastes, new 
low-chromium alloy and coating substitutes, corrosion- and oxidation-resistant stainless 
steels, and chromium-containing refractories. This report is a compilation of the papers 
presented at the briefing held at Corvallis, OR, June 4-5, 1985. 

Special recognition goes to Julie A. Searcy and her staff at the Oregon State Universi- 
ty, LaSells Steward Center, for their part in organizing and hosting the briefing activities. 
The assistance of Duggan Flanakin, Bureau of Mines, Division of Publication, in compil- 
ing the many manuscripts is gratefully acknowledged. 



PERMISSIONS AND INQUIRIES 



Information contained herein may be freely quoted, provided the author and these PRO- 
CEEDINGS are properly credited. Inquiries regarding individual papers should be directed 
to the respective authors. Inquiries regarding the overall Briefing should be directed to 
the compiler, Bureau of Mines, U.S. Department of the Interior, Albany Research Center, 
P.O. Box 70, Albany, OR 97321, U.S.A. 



CONTENTS 



Page 

Preface i 

Abstract 1 

General Session, George J. Dooley III, Presiding . . 3 
Chromium Contained in U.S. -Produced Stainless 

and Heat-Resisting Steels, by John F. Papp ... 5 
Chromite Resources -Market Economy Countries, 

by Edward H. Boyle, Jr., and Paul R. Thomas 13 
Chromite Resources in Alaska, by Jeffrey Y. 

Foley, James C. Barker, and Lawrence L. 

Brown 23 

Chromite Resources in the Conterminous United 

States, by Nicholas Wetzel 31 

Extractive Metallurgy Session, Charles B. Daellen- 

bach, Presiding 43 

Coproduct Chromite From Nickel-Bearing Lat- 

erites, by Donald E. Kirby and Donald R. 

George 45 

Characterization and Beneficiation of Domestic 

Chromite-Bearing Materials, by Lawrence L. 

Brown 51 

Flotation Beneficiation of Chromite From Low- 
Grade Deposits, by J. L. Huiatt 57 

A Chemical Method for Recovering Chromium 

From Domestic Chromites, by Gary L. Hundley 

and R. S. Olsen 63 



Page 

Pyrometallurgical Processing of Domestic Chromium 
Resources, by Ralph H. Nafziger 71 

Carbonyl Process To Upgrade Chromite Concen- 
trates, by A. Visnapuu and W. M. Dresell .... 77 

In-Plant Recycling of Chromium-Bearing Specialty- 
Steelmaking Wastes, by L. A. Neumeier and 

M. J. Adam 85 

Materials Session, Howard W. Leavenworth, Jr., 

Presiding 93 

An Overview of Chromium Needs and Uses, by 
Howard W. Leavenworth, Jr 95 

Chromium Alloy Coatings -A New Method of 
Preparation, by G. R. Smith, J. E. Allison, Jr., 
and W. J. Kolodrubetz 99 

Wear Protection of Iron-Base Castings by Cast-On 
Hard Surfacing, by Jeffrey S. Hansen 107 

Optimizing of Materials Selection Through Corro- 
sion Science, by D. R. Flinn 115 

Substitutes for Chromium in Corrosion- and 
Oxidation-Resistant Stainless Steels, by J. S. 
Dunning 125 

Wear- Resistant Alloys -Reducing Chromium Con- 
tent and Improving Wear Resistance, by Robert 
Blickensderfer 129 

Bureau of Mines Research Related to Refrac- 
tories Containing Chromium, by Arthur V. 
Petty, Jr 135 



CHROMIUM-CHROMITE: BUREAU OF MINES ASSESSMENT AND 

RESEARCH 

Proceedings of Bureau of Mines Briefing Held at Oregon State University, 

Corvallis, OR, June 4-5, 1985 



Compiled by Charles B. Daellenbach 1 




ABSTRACT 



This briefing was sponsored by the Bureau of Mines to summarize ongoing and recent- 
ly completed chromium-chromite research and resource assessment activities by the 
Bureau. Through the series of 18 presentations compiled herein, Bureau personnel covered 
a wide range of topics including U.S. chromite and chromium trends and usage patterns; 
foreign and domestic resources; and research activities on mineral characterization and 
beneficiation, chemical and pryometallurgical processing of chromite and chromium-bearing 
wastes, new low-chromium alloy and coating substitutes, corrosion- and oxidation-resistant 
stainless steels, and chromium-containing refractories. 



'Supervisory research metallurgist, Albany Research Center, Bureau of Mines, P.O. Box 70, Albany, OR 97321. 



GENERAL SESSION 

Chairman: George J. Dooley III 

Research Director 

U.S. Bureau of Mines 

Albany Research Center 

P.O. Box 70 

Albany, OR 97321 



BuMines IC 9087: Chromium-Chromite: Bureau of Mines Assessment and Research 



CHROMIUM CONTAINED IN U.S.-PRODUCED STAINLESS AND 

HEAT-RESISTING STEELS 

By John F. Papp 1 



ABSTRACT 



The primary objective of this Bureau of Mines study is 
to calculate an accurate, reliable Cr content of stainless and 
heat-resisting steel produced in the United States. Such a 
content is required for estimating the quantity of Cr 
recovered from recycled stainless steel and consumed by 
market sector. 

The Unified Numbering System is a unified identifica- 
tion system of chemical specifications for metals and alloys 
developed as a collective effort among organizations 
publishing specifications. This system defines the Cr com- 
position of U.S. -produced stainless and heat-resisting steels. 



The American Iron and Steel Institute's production data 
define the quantities of U.S. -produced stainless and heat- 
resisting steels. These Cr composition and production data 
were used to calculate the average Cr composition of 
stainless and heat-resisting steel produced in the United 
States from 1962 through 1983 as 16.7 pet. A historical 
series of the quantity of Cr contained in U.S. -produced 
stainless and heat-resisting steels was calculated, and those 
steels that accounted for the greatest amount of Cr were 
identified. 



INTRODUCTION 



The Bureau of Mines has reported Cr mineral produc- 
tion, consumption (I), 2 and availability {2-3) and has under- 
taken a supply-demand study. A result of the production- 
consumption report is apparent consumption (AC) 3 of Cr in 
the United States, a measure of national Cr consumption 
also called industrial demand. Chromium AC is compared 
with availability to determine adequacy of supply; it averag- 
ed 516,000 st/yr in the United States from 1973 through 
1983. U.S. production now consists only of secondary pro- 
duction measured as Cr contained in purchased stainless 
steel scrap. Imports, exports, and inventories are measured 
as Cr contained in chromite ore and concentrate, Cr fer- 
roalloys and metal, and Cr chemicals. 

The major Cr-consuming industries are the refractory 
industry, the chemical industry, and the metallurgical in- 
dustry. Chromite ore is consumed by the refractory in- 
dustry for its chromite mineral content, while the chemical 
and metallurgical industries consume chromite ore for its Cr 
content. Chromium ferroalloys are consumed by the 
metallurgical industry for their Cr content. Over the 
1973-83 time period the metallurgical industry accounted 
for 70 pet of industrial demand. Over the same time period 



1 Physical scientist, Division of Ferrous Metals, Bureau of Mines, ziOl E 
St., NW.. Washington, DC 20241. 

2 In each paper in these Proceedings, italic numbers in parentheses refer to 
items in the list of references at the end of that particular paper. 

3 Apparent consumption = primary production + secondary production + 
imports - exports + beginning inventories - ending inventories. 



the chemical industry accounted for 18 pet, and the refrac- 
tory industry for 12 pet, of industrial demand. Based on the 
1977-83 period, reported consumption of Cr materials by 
specific end use shows that stainless and heat-resisting 
(S&HR) steels account for 70 pet of the reported consump- 
tion. It is because S&HR steels account for 70 pet of 
metallurgical demand, which in turn accounts for 70 pet of 
industrial demand, that one can say: "As stainless steel 
goes, so goes chromium." 

For the purpose of computing U.S. apparent consump- 
tion, secondary production (i.e., the Cr contained in pur- 
chased S&HR steel scrap) is the only component of domestic 
Cr production, to calculate secondary production, the Cr 
content of S&HR steel is required, hereafter called 
Cr/S&HR factor. The primary objective of this work is to 
calculate an accurate, reliable Cr/S&HR factor. This conver- 
sion factor is also useful for estimating the quality of Cr con- 
sumed by market sector, recoverable by recycling, and re- 
quired to produce S&HR steel. 





Abbreviations Used in This 


Paper 


mt 


metric ton 




pet 


percent 




St 


short ton 




st/yr 


short ton per year 




yr 


year 





PROCEDURE 



METHOD 

The Cr content of S&HR steel production was 
calculated using Unified Numbering System (UNS) and 
American Iron and Steel Institute (AISI) data. This calcula- 
tion was carried out for the time period 1962-83. The 
Unified Numbering System for Metals and Alloys (4) de- 
fined the universe of S&HR steel grades and the Cr com- 
position limits of those grades. Annual AISI S&HR steel 
production by AISI Type data (5) defined production. To 
calculate the Cr content of S&HR steel, UNS Grades were 
associated with AISI Types; then constituent Grade Cr com- 
position defined Type Cr compositions. The Type Cr 
composition-production products were calculated and 
summed to get annual values. The Cr/S&HR factor was 
then calculated as the 1962-83 time average of the composi- 
tion average of maximum and minimum Cr content of 
S&HR steels divided by total S&HR steel production. 

Prior to calculating a historical series of chromium con- 
tained in S&HR steel in more detail than an aggregated an- 
nual total, it was necessary to combine AISI Types into 
Type Groups, hereafter called Groups. AISI reported pro- 
duction among 63 Types in combinations that varied from 
year to year, so Types had to be combined to form Groups 
for which a production value was available over the entire 
analysis period. (Exceptions to this definition are discussed 
below.) Having associated AISI Types into Groups for the 
analysis period, Group Cr compositions were calculated 
based on AISI Type Cr compositions. The Groups that ac- 
counted for the predominant amount of chromium use were 
identified by quantity used. The market classes, as iden- 
tified by the American Society for Metals (6'), were related 
to the Groups. 



AISI TYPES BASIS SET 

The S&HR steel categories about which the most de- 
tailed production data are available are the AISI S&HR 
steel Types. An AISI Type basis set was chosen to 
categorize 1962-83 S&HR steel production. The Type 
categories used by AISI to report production changed from 
the 1962-76 to the 1977-83 time periods. In 1977 AISI in- 
troduced many new specific Types and eliminated several 
descriptive Type categories. Table 1 contains definitions for 
specific and descriptive Types. In 1977 AISI introduced the 
specific Types 205, S30430, 304N, 316F, 316N, 317L, 329, 
330, 384, 409, 420F, 422, 429, 434, and 436; 406 and 443 
were eliminated. The eight descriptive categories under 
"Other chromium nickel stainless steels with:" were con- 
tracted into four descriptive categories under the name 
"Other Chromium Nickel Stainless Steels With:," and the 
"All other" category was subdivided into "All Other 15% 
Chromium or Less" and "All Other Over 15% Chromium." 

The objectives in choosing a basis set were to (1) take 
advantage of the similarities between the 1962-76 and the 
1977-83 sets, (2) eliminate rarely used categories, and (3) re- 
tain detailed production data. These objectives were 
satisfied by choice of the 1977-83 set to be the AISI Type 
basis set. This basis set contains 63 AISI Types, of which 55 
are specific Types and 8 are descriptive Types. 



Having chosen the AISI basis set as that of 1977-83, it 
was necessary to make the 1962-76 AISI S&HR steel pro- 
duction data consistent with 1977-83 Type set. This ration- 
alization is necessary because of the category name changes 
made by AISI as described above. Each of the resulting 
special cases is discussed below. No changes in the 200 
series or 300 series were required. In the 400 series, Types 
406 and 443 appeared during the 1962-76 period but not 
during the 1977-83 period. Throughout the 1962-76 period, 
AISI combined production to Type 406 with that of Type 
405. Except for 1965 and 1966, AISI combined production 
of Type 443 with that of Type 442. To adjust production 
values, Type 406 was treated as Type 405, and Type 443 
was treated as Type 442. Prior to 1977, each of the "Other 
chromium nickel stainless steels" categories was subdivided 
into two categories: one for other alloys under 10 pet, and 
one for other alloys over 10 pet. Except for 1966-69, AISI 
combined production of the other alloy under 10 pet and 
over 10 pet into a single value for each nickel category. That 
AISI combination procedure was used in this study. The 
1962-76 Type "All other" was subdivided into "All Other 
15% Chromium or Less" and "All Other Over 15% 
Chromium" in 1977. In this study all of the pre-1977 "All 
other" category production was treated as "All Other 15% 
Chromium or Less." The 1962-76 category "501, 502, and 
All Other high chromium heat resisting steels" was sub- 
divided into Types "501," "502," and "All Other High 
Chromium Heat Resisting Steels." In this study all of the 
pre-1977 "501, 502, and All Other High Chromium heat 
resisting steels," category production was treated as Type 
501. Because of the AISI 1977-83 basis set used here, a few 
production values from the 1960's had to be combined. 



TABLE 1.— Association of UNS Grades with descriptive AISI 
Types 1 

Descriptive 

AISI Type Unified Numbering System, Unified 
Number 

Other Chromium Nickel 
Stainless Steel With: 

Nickel under 8% S20300, S21400, S21460, S21600, 

S21603, S21900, S21904, S24000, 
S24100, S31100, S31500, S36200, 
S41008, S41025, S41800, S43035, 
S43036, S44020, S44023, S44300, 
S44400, S44625, S44626, S44700, 
S44800, S4500 

Nickel 8-16% S14800, S16800, S20910, S21800, 

S30310, S30330, S30345, S30360, 
S30490, S30452, S30940, S31609, 
S32109, S34709, S34720, S34723, 
S34809, S45500 
Nickel over 16-24% . . . S33100, S38100 

Chromium 15% or less S41040, S41610, S42023 

Chromium over 15% S18200 

All Other High Chromium 

Heat Resisting Steels S50300, S50400 

Production Not 

Shown By Type ! S13800, S15500, S15700, S17400, 

S17600, S17700, S35000, S35500, 
S42300 

1 A specific AISI Type is an alphanumerically named AISI Type category 
that specifies a single grade, such as Types 304, 304N, and 409. A descrip- 
tive AISI Type Is an AISI Type category whose name describes the 
category contents, such as Other Chromium Nickel Stainless With Nickel 
under 8%. 

1 PNSBT. This descriptive AISI Type name was Production Not 
Reported by Type (PNRBT) from 1962 through 1976. 






UNS GRADES TO AISI TYPES 

The largest single group of S&HR steel categories for 
which detailed chemical composition data are available are 
the UNS Grades. The UNS set of S&HR steels is composed 
of 116 Grades, each specifically numbered and having an 
elemental composition specification. Of these 116 UNS 
Grades, 115 are from the "Heat and Corrosion Resistant 
(Stainless Steels)" series and one is from the "Nickel and 
Nickel Alloys" series. The UNS Grades were distributed 
over the AISI Type basis set to define the Cr composition 
limits of the AISI Types. 

Only one UNS Grade corresponded to each of the 55 
specific AISI Types. For these 55 Types, the Type Cr com- 
position is the same as the corresponding Grade Cr com- 
position. There were multiple UNS Grades for seven of the 
remaining eight descriptive AISI Types. For one descriptive 
AISI Type (Nickel Over 24%), there was no USN Grade. 
The association of UNS Grades that correspond to specific 
AISI Types is straightforward because the USN Grades are 
cross-referenced with AISI Types (4). Those UNS Grades 
were assigned first. The remaining UNS Grades then 
belonged to one of the descriptive AISI Type categories. 
These remaining UNS Grades were distributed among the 
descriptive AISI Types as follows: 

1. All UNS Grades that had no AISI Type name were 
assigned to the "Other Chromium Nickel Stainless Steels" 
Types if they contained nickel, or to the "All Other" Types if 
they were nickel-free. 

2. All UNS Grades that had an AISI Type name were 
assigned to the "Production Not Shown By Type" (PNSBT) 
Type. 

Table 1 details the result of these associations. In each 
case where more than one UNS Grade contributed to an 
AISI Type, the constituent Grade Cr compositions were 
averaged to obtain the Type Cr composition. 

Having defined the AISI Type basis set Cr content via 
UNS Grades and production via AISI S&HR steel pro- 
duction reports, the Cr/S&HR factor can be calculated. Let 
Cr mj be the fractional Cr content of Type i, where m 
represents minimum, median, or maximum. Let P- be the 
AISI S&HR steel production reported as Type i in year j. 
Then F, the Cr/S&HR factor, was calculated as 



; n 1977 and combined with Type 304 in 1980, 1982, and 
1983. To have rigidly adhered to the Group definition would 
have meant assigning Type 304 to PNSBT Type category, 
when S30430 production was only 2 pet of that of Type 304. 
Both Group production and Cr composition were defined by 
those of the constituent Types. 

Over the time period of this analysis, AISI published 
production data for most AISI Types, although not for each 
Type each year. Since production data were available, those 
data were used to define the relative importance of the con- 
tribution of each AISI Type to a Group. The relative im- 
portance, the weight factor, was calculated as the 
production-based fractional contribution of each AISI Type 
to its Group. The fraction, for a given year, is the production 
for an AISI Type divided by the Group production and is 
called the annual weight factor. 

Thus, the Cr composition of a Group is defined as the 
production-based, weighted average of the constituent AISI 
Types times the Cr composition of constituent AISI Types 
summed over the constituent Types. For example, suppose 
that a Group is composed of three AISI Types; the Type i 
production in year j is Pij and Group g production in year j is 



P*/=£p.> 



(1) 



The annual weight factor for Type i in year j is w-j = P^/P -. 
Let the uniqueness of Type i reported production in year j be 



_0 for composite production, or 
,J ~1 for unique production. 

Here composite means Type i reported production in year j 
was combined with that of another Type(s). Unique means 
Type i reported production in year j represented only Type i. 
Let 



1983 

U,= £ u, y 

j = 1962 



1983 63 1983 63 

F„=[ £ £ Cr„,p, y ]/ £ £ p„. 

j- 1962 i=l j = 1962 i = l 



Cr m - is the fractional Cr content of Type i, where m is 
minimum, median, or maximum; the Cr composition of 
Group g is defined as 



AISI TYPES TO GROUPS 

To produce a historical series of chromium contained in 
S&HR steel in more than annual aggregate detail, many 
AISI Types had to be collected into Groups that have an an- 
nual production value composed of the same AISI Type pro- 
duction values over the entire analysis period. 

The necessity to combine Types into Groups results 
from AISI's variation of (1) Type categories and (2) Types 
among which production was collected. To collect as few 
Types as possible together, when the effect of combined pro- 
duction was small, the Types were not combined and the 
definition of Groups set forth above was not strictly fol- 
lowed. Groups 201, 304, 317, and 429 were affected. For ex- 
ample, S30430, a constitutent of Group 304, was introduced 



Cr„,= £ £ [Cr., w„ u y /U,]. 

j = 1962 i=l 



Interchanging the sums over i and j, and defining the 
average weight factor as 



1983 

W,=( £ w u JU h 

j=1962 



one obtains 



Cr m ,= £ W,Cr m „ 

i = l 



(2) 



This example illustrates the computation method used to ob- 
tain Group production, equation 1, and Group Cr composi- 
tion, equation 2. 

Actual computation differed in that- 

1. The number of AISI Types that make up a Group 
varied from as few as one to as many as nine. 

2. Average weight factors were calculated for two time 
periods, 1962-76 and 1977-83. 



3. A few special cases arose where the constituent Type 
weight factor had to be assumed owing to lack of production 
data. 

The association of AISI Types into Groups and the 
resulting Cr compositions (minimum and maximum Cr frac- 
tions) are shown in table 2. From 63 AISI Types, 33 Groups 
were formed. 



TABLE 2.— Chromium compositions of the Groups and their constituent AISI Types ' 





Chromium fraction 




AISI Type and Group Name 


Chromium fraction 


AISI Type and Group Name 


Minimum 


Maximum 


Minimum 


Maximum 


201 Group 

201 Type 

202 Type 


0.1607 
.1600 
.1700 
.1600 

.1680 
.1700 
.1700 
.1500 

.1200 
.2300 
.1200 

.1615 

.1168 
.1150 
.1150 
.1200 
.1200 

.1600 
.1400 
.1600 


0.1807 
.1800 
.1900 
.1800 

.1880 
.1900 
.1900 
.1700 

.1400 
.2600 
.1400 

.1817 

.1368 
.1350 
.1350 
.1400 
.1400 

.1800 
.1600 
.1800 




442 Group 


0.2281 
.1800 
.2300 

.1386 
.1183 
.1750 

.1534 
.1700 
.1600 
.2300 
.1700 
.1050 
.1200 
.1150 
.1600 
.1600 
.1442 


0.2685 


442 Type 

446 Type 

Cr(Ni - O) Group 


.2300 
.2700 


205 Type 




347 Group 

347 Type 

348 Type 

384 Type 

Ni.GT.16-24% Group 

314 Type 

Ni GT.16-24% Type 2 . . 


.1586 


Cr.LE. 15% Type 3 

Cr.GT. 15% Type 4 

NRBT Group 

316F Type 


.1383 
.1950 

.1761 
.1900 


316N Type 


.1800 




329 Type 


.2800 


Ni.GT.24% Group 


330 Type 

409 Type 

420F Type 


.2000 
.1175 
.1400 • 


410 Group 

410 Type 

414 Type 

416 Type 

416 Se Type 

429 Group 


422 Type 

434 Type 

436 Type 

PNSBT Type 5 


.1350 
.1800 
.1800 
.1586 






429 Type 

430 Type 





' The following Groups are composed of one AISI Type of the same name: 301, 305, 308, 309, 309S, 316, 316L, 321, Ni under 8%, Ni 8-16%, 
403, 405, 420, and 431. The following Groups are composed of AISI Types (shown in parentheses) of the same minimum and maximum chromium 
fraction contents: 302 Group (302 + 302B), 303 Group (303 + 303Se), 304 Group (304 + S30430), 304N Group (304 + 304L), 310 Group (310 + 310S), 317 
Group (317 + 317L), 430F Group (430F + 430FSe), 440A Group (440A + 440B + 440C), 501 group (501 + 502, and Other Group (All Other High Chromium 
Heat Resisting Steels, which is S50300 + S50400). 

There are small changes in content fraction from the 1962-76 time period to the 1977-83 time period for a few Groups. These changes result 
from changes in the AISI production reporting practice between those time periods. The values reported here are the 1977-83 values. 

2 Other Chromium Nickel Stainless Steels With: Nickel over 16-24%. 

3 All Other, 15% Chromium or Less. 

4 All Other, over 15% Chromium. 

5 Production Not Shown By Type. 



RESULTS 



Over the 1962-83 period, the content of S&HR steel pro- 
duced was calculated based on the minimum, average, and 
maximum Cr fractions per AISI Type. The resulting 
minimum Cr content was 0.1574; average, 0.6171; and max- 
imum, 0.1768. Thus, the Cr/S&HR factor was found to be 
0.1672 ±0.0097. The Cr/S&HR factor of 0.1671 was found 
to have a mean square deviation of 0.0004 over the time 
period. This average Cr fraction represents about 5,768,000 
st Cr contained in about 34,518,000 st of S&HR steel pro- 
duction. 

Over the analysis time period (1962-83) only one of the 
33 Groups accounted for a substantial fraction of Cr con- 
tained in S&HR steel production. The 304 Group, composed 
of AISI Type 304 and S30430, accounted for 36 pet of the Cr 
contained in production. Three Groups (i.e., 304 Group, 
NRBT Group, and 301 Group) accounted for 53 pet of the Cr 
contained in S&HR steel production. Only 13 Groups ac- 
counted for 90 pet of the Cr. Table 3 summarizes these 
results. At 36 pet, the 304 Group accounts for the largest 
share. This contribution is more than four time greater than 



TABLE 3.— Summary of chromium contained in S&HR steel 
production by Group in descending order of chromium con- 
tained in production for the analysis period 1962 through 1983 





S&HR steel 

production ' 

st 


Cr 

content of 

production 

st 


Cr content, 
pet of total 


Group name 


Group 


Accumu- 
lated 


304 

NRBT 


11,373,020 

3,051,374 

2,833,684 

2,686,547 

2,078,918 

1,634,761 

1,900,017 

1,164,646 

971,967 

831,776 

876,236 

867,138 

532,134 

3,715,925 


2,160,099 
502,756 
481,726 
456,713 
308,950 
277,909 
240,891 
221,283 
186,169 
149,720 
148,960 
148,066 
95,784 
585,627 


36.2 
8.4 
8.1 
7.7 
5.2 
4.7 
4.0 
3.7 
3.1 
2.5 
2.5 
2.5 
1.6 
9.8 


36.2 
44.6 


301 

429 

Cr(Ni-O) 

316 


52.7 
60.4 
65.6 
70.2 


410 


74.3 


304N 


78.0 


Ni.LT.8% 


81.1 


303 

316L 

201 

302 

Remaining 20 


83.6 
86.1 
88.6 
90.2 
100.0 


Total 


34,518,143 


5,964,653 





1 American Iron and Steel Institute AIS 104 reports for 1962-83. 



that of the next nearest Group. The Cr share of the next 
three Groups is similar, each Group accounting for about 8 
pet of the Cr contained in S&HR steel production. 

Figures 1 and 2 detail the chromium contained in S&HR 
steel production for the seven Groups that accounted for 74 
pet of the Cr. These figures show the quantity of Cr con- 
tained in Group production by year for each of the seven 
Groups. It is apparent from these figures that there are fair- 
ly large variations in the quantity of Cr contained in S&HR 



steel production from year to year. These variations are due 
primarily to changes in annual production. The NRBT and 
Cr(Ni = 0) Groups show significant changes, in opposite 
directions, between 1976 and 1977. The AISI Type composi- 
tion of these two Groups is shown in table 2. The composi- 
tion of the PNSBT Type changed significantly in 1977 when 
many specific Type categories were introduced -pre- 
sumably separated from the 1962-76 PNRBT category. 



160 



140 - 



20 



i 1 r 

304 Group 




NRBT Group 



_L 



A ■ • ■ - 

i \ . 

/\ / i /Cr (Ni=0) Group 



j i Ilr 



1962 1964 1966 1968 1970 1972 1974 1976 1978 1980 1982 1984 
FIGURE 1.— Chromium contained in S&HR steel production. Groups 304, Cr(Ni = 0), and NRBT by year. 




Q 

o 
rx 

Q. 10 



'/v * >- 

J \410 Group 



\i 



J_ 



_!_ 



J L 



J L 



1962 1964 1966 1968 1970 1972 1974 1976 1978 1980 1982 1984 
FIGURE 2.— Chromium contained in S&HR steel production. Groups 301, 316, 410, and 429 by year. 



10 



DISCUSSION 



Together, AISI Types 304 and S30430 make up Group 
304. AISI Type 304 has been described (6) as a low-carbon 
modification of AISI Type 302. The carbon is lower to 
restrict carbide precipitation during welding. The major end 
uses of Type 304 are chemical and food processing equip- 
ment, brewing equipment, cryogenic vessels, gutters, 
downspouts, and flashing. Type S30430 work-hardens less 
readily than does Type 305, and thus finds major use in 
servere cold-heading applications. 

Group 304 accounts for by far the greatest amount of Cr 
contained in S&HR steel production. The large quantity of 
Group 304 production suggests a variety of end uses and, 
therefore, a variety of reasons for using this steel. The large 
quantity of Group 304 production suggests that this 
material is likely to be a major constituent of S&HR steel 
scrap. The large quantity of Group 304 production suggests 
that Group 304 is likely to account for a large share of recy- 
cled stainless steel scrap. 

Between 1976 and 1977, the Cr contained in NRBT 
Group production rose sharply, while that of Cr(Ni = 0) 
Group declined sharply (fig. 1). The author concluded that 
these 1976-77 production changes resulted from the move- 
ment of Type 409 production from the Cr(Ni = 0) Group dur- 
ing 1962-76 to the NRBT Group during 1977-83. This move- 
ment occurred because Type 409 production was listed in 
the 1962-76 "All other" category, which was associated with 
the Cr(Ni = 0) Group; but in 1977 it was associated with the 
NRBT Group when Type 409 became a specific AISI Type 
used to report production. One cannot know with certainty 
the allocation of Grades and Types among descriptive AISI 
Type categories, because such information is not published. 
The following points are offered in support of the conclu- 
sion: 

1. The general organization of the AIS 104 Form sug- 
gests that 400 series stainless steels not specifically listed 
belong in the "All other" category. 

2. The sharp NRBT and Cr(Ni = 0) Group Cr content 
1976-77 changes are not characteristic of the remainder of 
the Cr content time series for either Group, before or after 
the 1976-77 changes. 

3. Type 409 is a stainless steel used primarily in 
automobiles. Its automotive use increased in the 1970's and 
is thought to have changed from little to extensive during 
the 1973-75 period. Increasing Cr content of production for 
the Cr(Ni = 0) Group and decreasing content for the NRBT 
Group over the 1970-76 period implies that the increasing 
Type 409 production was included in the Cr(Ni = 0) Group 
category during the 1962-76 period. 

4. The changes in association of Type 409 production 
from the Cr(Ni = 0) to the NRBT Group in 1977 would ac- 
count for the 1976-77 changes of both Groups. 

Until about 1970, Type 409 was only used for parts in 
automobile exhaust system components. Its use then in- 
creased when automobile manufacturers elected to comply 
with the Federal Clean Air Act of 1970 by equipping 
automobiles with catalytic converters. Type 409 provided 
the desired lifetime for these converters at the higher 
operating temperatures resulting from converter use. By 
1975, the majority of automoblies were equipped with 
catalytic converter exhaust systems (9). 



Because the Type Cr compositions are average in form- 
ing a Group, one might expect little effect on the Cr com- 
position of a Group to result from the assignment of one or 
two Types to a Group category of several constitu tents. 
Such is not the case for the association of Type 409 with the 
NRBT Group or the Cr(Ni = 0) Group because Type 409 pro- 
duction is very large and has a low Cr fraction (0.1050 to 
0.1175) compared with the S&HR steel average of 0.1671. 
The false nature of such a supposition is shown by calcula- 
tion of the average Cr content of S&HR steel based on the 
Group data in table 3. Such a calculation yields an erroneous 
average Cr value 3 pet greater than the recommended value 
of 0.1671. 

Based on the methodology described, the average Cr 
fraction of S&HR steel production was calculated to be 
0.1671, with a mean square deviation of 0.0004 and a 
chemical composition specification uncertainty of ±0.0097. 
The consistency of this value over the time period suggests 
that this value could be reliably used to estimate the secon- 
dary Cr production component of apparent consumption. 
Secondary Cr production is Cr contained in purchased 
stainless steel scrap. In-house scrap is not a Cr production 
source for the purpose of computing apparent consumption. 

The quantity of purchased scrap is the subject of a 
Bureau of Mines industry survey. The results of that survey 
are published monthly in the Iron and Steel Scrap Mineral 
Industry Surveys and annually in the Minerals Yearbook. 
Until 1983, a Cr/S&HR factor of about 12 pet was used to 
estimate secondary Cr production. In 1982, a cursory study, 
similar to the one on which the results in this paper are 
based, estimated the Cr/S&HR factor at about 0.16. 
Therefore, in 1983, secondary production was estimated us- 
ing about 0.16 to calculate the Cr content of purchased 
stainless steel scrap. The National Materials Advisory 
Board (NMAB) (7) has suggested 16.4 pet, and a Bureau 
study (8) 16.7 pet, for the average Cr content of S&HR steel. 
NMAB does not explain its methodology, rendering impossi- 
ble a critical comparison between the value reported here 
and that reported by the NMAB. The value reported in IC 
8822 (8) was determined by multiplying the median Cr com- 
positon by production for the years 1957 and 1977. The 
methodology of IC 8822 differs from that of this study in 
that- 

1. IC 8822 (table A-3, p. 41) identifies the Cr composi- 
tion of AISI Types 430, 430F, and 430F Se as 14.00 to 18.00 
pet. The UNS composition used here is 15.00 to 18.00 pet. 

2. IC 8822 does not specify Cr compositions for the AISI 
Types 329, 409, 422, 434, 436, and 442. These grades were 
apparently disregarded in the computation of average Cr 
content. 

3. IC 8822 makes no Cr composition definition for the 
descriptive categories "Nickel Under 8%," "Nickel 8-16%," 
"Nickel Over 16-24%," "Nickel Over 24%," "All Other High 
Chromium Heat Resisting Steels," and "PNRBT." 

4. The data base used in IC 8822 (2 yr) is small compared 
with that used in this study (22 yr). 

Although IC 8822 does not specify chemical composi- 
tions for AISI Types 304N, 316F, 416, and 420F, it does 
have chemical compositions for AISI Types of the same 
number series. For example, IC 8822 includes Types 304 
and 304L, but not 304N. 



11 



Among this author's objectives in calculating the 
average Cr content of S&HR steel were to (1) use as much 
of the detailed Type composition and production data as 
possible, (2) take advantage of the similarity of AISI annual 
production reports and the consistency of AISI Type Cr 



composition, and (3) account for production categorized by 
descriptive AISI Types. Short of treating each year's pro- 
duction on an individual basis, this approach represents the 
most thorough use of available data. 



CONCLUSION 



Three conclusions appear apporpriate from the 
preceding results and discussion. First, the factor 
0.1671 ± 0.0097 should be used to calculate the Cr content of 
stainless and heat-resisting steel unless specific Cr com- 
position information is available. Second, in combining AISI 
Types into Groups of consistent historical constitutent 
structure, the 400 series AISI Types that first appeared in 
1977 (i.e., Types 409, 420F, 422, 429, 434, and 436) should 
be asociated with the Cr(Ni = 0) Group. Third, the criteria 
used to associate UNS Grades with AISI Types should be 
modified. As done in this study, all UNS Grades that corre- 
spond to a specific AISI Type should be so associated. The 



difference comes in distributing the remainder of the UNS 
Grades among the descriptive AISI Types. All remaining 
100-300 series UNS "Heat and Corrosion Resistant" steels 
should be associated with the AISI "Other Chromium Nickel 
Stainless Steel" Types; and all remaining 400 series should 
be associated with the AISI "All Other 15% Chromium or 
Less" and "All Other Over 15% Chromium" Types. As done 
in this study, all remaining 500 series should be associated 
with AISI "All Other High Chromium Heat Resisting 
Steels." This leaves no Grades for the "PNSBT" Type.. This 
Type category should be presumed to have a composition 
equal to the average of the other categories. 



REFERENCES 



1. Papp, John F., Chromium. Chapter in Mineral Facts and Prob- 
lems, 1985 Edition. BuMines B 675, 1985, pp. 139-156. 

2. Lemons, J. F., E. H. Boyle, Jr., and C. C. Kilgore. Chromium 
Availability -Domestic. A Minerals Availability System Appraisal. 
BuMines IC 8895. 1982. 14 pp. 

3. Thomas, P. R., and E. H. Boyle, Jr. Chromium Avail- 
ability -Market Economy Countries. A Minerals Availability Pro- 
gram' Appraisal. BuMines IC 8977, 1984, 86 pp. 

4. . Unified Numbering System for Metals and Alloys. 

Society of Automotive Engineers, Inc., 2d ed., Sept, 1977, pp. 
159-169. 

5. American Iron and Steel Institute. Fourth quarter reports of 
AIS Form 104, Quarterly Production of Stainless and Heat 
Resisting Raw Steel. 



6. Metal Progress. Material and Processing Data Book. American 
Society for Metals, Metals Park, OH 44073. Various issues. 

7. National Materials Advisory Board. Contingency Plans for 
Chromium Utilization. Natl. Acad. Sci., NMAB-335, 1978, p. 128. 

8. Kusik, C. L., H. V. Makar, and M. R. Mounier. Availability of 
Critical Scrap Metals Containing Chromium in the United States. 
Wrought Stainless Steels and Heat Resisting Alloys. BuMines IC 
8822, 1980, appendix A, pp. 38-44. 

9. Peckner, D., and I. M. Bernstein. Handbook of Stainless 
Steels. McGraw-Hill, 1977, p. 39-11. 



BuMines IC 9087: Chromium-Chromite: Bureau of Mines Assessment and Research 



13 



CHROMITE RESOURCES— MARKET ECONOMY COUNTRIES 

By Edward H. Boyle, Jr. 1 and Paul R. Thomas 2 



ABSTRACT 



The Bureau of Mines has analyzed the long-term total 
cost and availability of chromite and high-C ferrochromium 
from 80 operations or deposits in 10 market economy coun- 
tries (1). The appraisal presented economic evaluations for 
the extraction of 1.2 billion mt of in situ demonstrated 
resources of chromite ore contained within the 80 opera- 
tions or deposits and addressed the long-term production 
potential of each of the 10 nations involved. It was 



estimated that approximately 649 million mt of marketable 
chromite products could be produced from the in situ 
demonstrated resource. 

This paper summarizes the overall availability of 
chromite products and high-C ferrochromium from the 
demonstrated resources as of the early 1980's for the 10 
countries and addresses specific resource aspects for each. 



INTRODUCTION 



This paper is a brief summary of the chromite resource 
position and of production potential for chromite and fer- 
rochromium in 10 major chromite-producing market 
economy countries (MEC's): Republic of South Africa, Zim- 
babwe, Turkey, Philippines, India, Brazil, Finland, New 
Caledonia, Greece, and Madagascar. Two introductory com- 
ments are necessary to explain the context of the coverage 
involved in this paper. 

First, although the 10 countries represented 99.2 pet of 
total 1982 MEC chromite production, they represented only 
about 50 pet of total world production of chromite in 1982. 
This is because two centrally planned economy country 
(CPEC) producers, the U.S.S.R. and Albania, were not 
analyzed. These two CPEC countries accounted for a com- 
bined 48 pet of world production in 1982 and have been, 
respectively, the first- and third-ranked world producers 
since 1981. They were not included in the analysis because 



'Physical scientist. 

Economist. 
Minerals Availability Field Office, Bureau of Mines, Building 20, Denver 
Federal Center. Denver, CO 80225. 



of a lack of comprehensive and detailed information on their 
chromite and ferrochromium industries and because the dif- 
ferences between MEC and CPEC economic systems pre- 
cluded any meaningful comparative cost analyses. 

Second, table 1 presents a list of major, undeveloped 
MEC chromite deposits that were not analyzed in the study 
because of a lack of detailed data, and thus are not included 
in any of the total available tonnages discussed in this paper. 
For the reasons shown in the last column of table 1, it is not 
likely that these deposits will be developed in the near 
future owing to economics or, more importantly, because of 
marketability (usage) problems. 



Abbreviations Used in This Paper 


km 2 


square kilometer 


m 


meter 


mt 


metric ton 


mt/yr 


metric ton per year 


pet 


percent 


yr 


year 



14 



TABLE 1.— Chromite resources, market economy countries 1 



Country 



Deposit 



Type of resource 



Estimated in situ 
tonnage, 10 3 mt 



Grade 
pet CrA 



Cr-Fe 
ratio 



Problems and status 



Australia Coobina High-grade, 

podiform- 
type deposits. 

Canada Winnepeg District . Low-grade, seam- 
type deposits. 
Greeland Fiskenaesset do 

Indonesia None announced . . Residual deposits 

and laterites. 



Papua New 
Guinea. 


Ramu River 


....do 


South Africa, 
Republic of. 


East and West 
Bushveld Complex. 


UG2 seam 



2,100 


28-49 


1.5 


Remote location, 
refractory-grade 
material. 


18,600 


8.7 


1.0-1.48 


Very low Cr-Fe ratios. 


2,500 


20-26 


1.0-1.2 


Remote location, very 
low Cr-Fe ratio. 


NA 


NA 


NA 


Exploration being 
conducted for low- 
grade eluvial chromite 
deposits. Also 
chromite In Nl-Co 
laterites. 


00,000 


5-10 


NA 


Remote location, 
low-grade, some of 
economics will depend 
on Nl-Co laterite 
technology and 
economies. 


30,000 


5.5 


1.2-1.3 


Extractable at certain 
operations on the 
Complex, but economic 
and marketing aspects 
questionable. Low 
Cr-Fe ratio of 
concentrate product. 
More promising for 
platinum values. 



NA Not available. 

' Not evaluated in this study for product availability or costs. Major questions of geology, economics, technology of extraction, or marketability 
raise doubts about production for the near term. In addition to these nondeveloped resources, other countries such as Cyprus, Iran, Japan, Pakistan, 
and Sudan produce very small amounts of chromite (140,000 mt combined production for 1980, including 82,000 mt of Iranian production). 



AVAILABILITY OF CHROMITE PRODUCTS AND 
HIGH-CARBON FERROCHROMIUM 



As shown in table 2, there are many ways to classify a 
particular chromite deposit and the products to be extracted 
from it, depending upon the criteria used for the classifica- 
tion. In table 2, the first four classification criteria (usage, 
Cr-Fe ratio, Al 2 3 content, and product size) are product- 
related as well as interrelated, while the last two criteria 
(geologic structure and mineralogic occurrence) are deposit- 
related and interrelated. 



TABLE 2.— Various classifications of chromite ores and 
concentrates in relation to classification criteria 

Usage Metallurgical, chemical, refractory. 

Cr-Fe ratio High-Fe, high-Cr. 

Al 2 3 content Refractory, nonrefractory. 

Product size Lump ore, fines (friable) ore, concentrates. 

Geologic structure . Podiform, stratiform, eluvial-alluvial- 

lateritic. 

Mineralogy Massive, disseminated, schlieren. 



As shown in figure 1, the 1.2 billion mt of in situ ore that 
has been cost-evaluated and forms the base of the results 
mentioned in this paper represents only 17 pet of the total 
demonstrated resources in the 10 countries. The difference 
is almost entirely represented by non-cost-evaluated 
demonstrated tonnages in the Great Dyke of Zimbabwe and 
the Bushveld Complex of South Africa. As such, the 
resource analyzed is very conservative. 

Figure 2 summarizes the demonstrated resources of 
recoverable chromite ore and concentrates (products), as 
analyzed in this study, according to the Cr-Fe ratio in prod- 
ucts that could be used for metallurgical purposes and the 



tonnage that was indicated to have specific refractory 
markets as of 1980. Approximately 260 million mt of high- 
Cr (>2.0 Cr-Fe ratio) products are available for metal- 
lurgical use, and 372 million mt of high-Fe (< 2.0 Cr-Fe 
ratio) products are available for metallurgical or chemical 
use. In addition, about 17 million mt of refractory-grade and 
foundry sand chromite products were estimated to be 
available from a select few of the mines and deposits ana- 
lyzed. This combined 649 million mt of available chromite 
products would represent 134 yr of production at 1982 
levels from all producing nations excluding the U.S.S.R. and 
Albania. 

Figure 3 shows the distribution of the combined 632 
million mt of high-Cr and high-Fe products according to 
their presence in either stratiform, podiform, podiform- 
stratiform (basically unclassified), and eluvial-alluvial- 
lateritic type deposits. The stratiform deposits (represented 
by the Bushveld Complex in South Africa, the Greak Dyke 
in Zimbabwe, the Campo Formosa District in Brazil, and the 
Kemi operations in Finland) contain 87.2 pet of the chromite 
products estimated to be available. The podiform deposits 
(represented by the Selukwe and Belingwe Districts in Zim- 
babwe, the Hassan District in India, the high-grade Philip- 
pine deposits, the large majority of the Turkish deposits, 
and the chromite deposits in Madagascar, New Caledonia, 
and Greece) account for only 5.2 pet of the total amount of 
products. The podiform-stratiform deposits (represented by 
the Cuttack, Dhenkenal, and Keonjhar Districts in Orissa 
State, India) account for 6.5 pet, and eluvial-alluvial-lateritic 
deposits in the Philippines and Zimbabwe represent only 1.1 
pet of the total amount of available chromite products. The 



15 





17 pet of total demonstrated 
resource of 10 nations studied; 
4 pet of world identified level 



FIGURE 1.— Relationship of cost-evaluated tonnage to an estimate of the total demonstrated and identified resource levels 
within the 10 nations under study. 



High -alumina 
2.6 pet 




FIGURE 2.— Total estimated available high-Cr, high-Fe, and 
refractory chromite products. 

bar graph of figure 3 presents these relative proportions in a 
more dramatic fashion. 

The preponderance of products from stratiform 
deposits shown in figure 3 would be significantly larger ex- 
cept for the limitations (see figure 1) put on the resource- 
cost analysis of the demonstrated chromite resource poten- 
tial of the Bushveld Complex in South Africa and the Great 



Dyke seam deposits in Zimbabwe. Even with this limitation, 
the importance of Zimbabwe and South Africa to the total 
available chromite products in both the high-Cr and high-Fe 
categories is in great evidence, as shown in the bar charts of 
figure 4. 

In the course of the analysis, it was realized that the 
utilization and economics of producing high-C fer- 
rochromium from these available chromite products would 
have to be addressed. Figure 5 presents a simplified rela- 
tionship between the Cr-Fe ratio in a particular chromite 
product and the grade of high-C ferrochromium that could 
be produced by the smelting of that chromite product. In 
this diagram, a grade C, high-C ferrochromium of 50 to 55 
pet contained Cr can be produced from a chromite ore or 
concentrate with a Cr-Fe ratio of 1.4 to 1.8, while a 56- to 
64-pct-contained-Cr, grade B, high-C ferrochromium can be 
produced from 1.8 to 2.45 Cr-Fe ratio chromite products, 
and a > 64-pct-contained-Cr, grade A, high-C ferro- 
chromium can be produced from ores and concentrates with 
Cr-Fe ratios exceeding 2.45. 

Applying this simplified relationship to the 80 mines or 
deposits analyzed gives the ferrochromium data shown in 
figure 6. If the entire 632 million mt of available high-Cr and 
high-Fe chromite products were smelted to produce high-C 
ferrochromium products, it would result in production of 
280 million mt of high-C ferrochromium. Of this total, the 
majority (173.6 million mt) would be grade C ferro- 
chromium, 44.3 million mt would be grade B ferro- 
chromium, and 61.9 million mt would be grade A ferro- 
chromium. South Africa represents 95 pet of the available 
grade C ferrochromium, Zimbabwe represents 87.3 pet of 
the available grade A ferrochromium, and South Africa and 
India represent 55 pet and 40 pet, respectively, of the 
available grade B ferrochromium. 



16 



ID 
O 



I- 

o 

r> 

Q 

O 

cr 
a. 



bUU 
















500 










400 


- 


E 






400 




o 
o 










OT 


£ 
o 


o 

+3 


200 






form-strati 
orm 


a> 

a 

"5 

"> 


100 






Podi 
Pod if 


I 
o 

> 

3 














< 























1 ' 



Podiform 
5.2 pet 
Pod if orm -stratiform 
6.5 pet 



Alluvial-eluvial-lateritic 
I.I pet 




FIGURE 3.— Total estimated available high-Cr and high-Fe products; distribution by product type. 



I40 r 



120 



ID 

o 



o 

3 
Q 

o 
rr 
o_ 



100 



80 



60 



40 



20 



KEY 
E%^ Others 

Madagascar 
Turkey 



o 



: : : : : : : : : : : : : : : : : : Philippines 
I India 



I/////1 



883 



High-Cr chromite 
(260 million mt) 



350r 



300 



250 



ID 

O 200 



o 

3 
Q 
O 
01 

a_ 



150 



100 



50 - 





High-Fe chromite 
(372 million mt) 



FIGURE 4.— Total estimated available high-Cr and high-Fe products; distribution by country. 



66 



64 



^ 62 
>" 

O 

_) 60 



O 
o 



58 



O 

rr 
cr 

W 56 



— 54 

Q 

Ld 

< 



50 



48 



17 



Grade C 



(50-55 pet Cr) 

High-Fechromite 



Grade B 
(56-64 pet Cr) 



Grade A _, 
(over 64 pet Cr) 



High-Cr chromite 



1.2 1.3 1.4 



1.6 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 
Cr-Fe RATIO IN CHROMITE PRODUCTS 



FIGURE 5.— Relationship between Cr-Fe ratio of chromite ores and Cr contained within a high-C 
ferrochromium product. 




Total = 280 million mt 

FIGURE 6.— Percentage contribution, by country, to total high-C ferrochromium availability estimates 
by product grades A, B, and C 



18 



SUMMARY, BY COUNTRY 



The following pages summarize pertinent aspects of 
chromite and ferrochromium availability in the 10 countries 
that were analyzed. 

REPUBLIC OF SOUTH AFRICA 

1. The Bushveld Complex contains all of the available 
chromite resource that was analyzed. 

2. An estimated 104.4 million mt of high-Cr chromite 
products and 307.6 million mt of high-Fe chromite products 
are available. This constitutes an immense resource of 
relatively low-cost chromite products. 

3. The analysis was limited to producing operations as 
of 1979-80 and to vertical depths of 300 to 600 m. This 
resulted in only about 20 pet of the total demonstrated 
chromite resource being analyzed for costs. (See figure 7.) 

ZIMBABWE 

1. There are four historical sources of chromite produc- 
tion: 

A. Seam deposits of the Great Dyke. 

B. Podiform deposits of the Selukwe District. 

C. Podiform deposits of the Belingwe District. 

D. Eluvial (residual) deposits in the northern por- 
tion of the Great Dyke. 

2. An estimated 116.7 million mt of products are 
available from Great Dyke seam deposits, 12.7 million mt 
from podiform deposits, and 0.8 million mt from eluvial 
deposits. All products are high Cr at 2.0 to 3.8 Cr-Fe ratios. 

3. Approximately 130 million mt of chromite products 
are available; however, the majority of the Great Dyke 
chromite resource (seam-stratiform) is relatively high cost. 

4. Analysis of Great Dyke seam deposits was limited to 
certain sections known to have had producing operations in 
1979-80 or in the past. As a result, only about 47 pet of the 



most commonly accepted total Great Dyke resource 
estimate was analyzed. 

5. Podiform deposits have good economics but limited 
resources; seam deposits have virtually unlimited resources 
but relatively poor economics. 

TURKEY 

1. The country has approximately 23,000 km 2 of 
ultramafic rock outcrops which could serve as hosts for 
chromite deposits. 

2. The Government exploration agency has identified 
over 330 individual chromite deposits or deposit groups in 
40 of Turkey's 67 Provinces and in at least 90 separate 
regions or districts (2-3). 

3. The tonnage evaluated represents the demonstrated 
resources in only 25 individual deposits at 6 major mining 
operations, and it should be considered as a very conser- 
vative appraisal of Turkey's chromite potential. 

4. Total in situ ore tonnage was estimated at 11.7 
million mt ore at a weighted-average Cr 2 3 grade of 38.0 
pet. This tonnage would result in production of about 7.6 
million mt of high-Cr chromite products with Cr-Fe ratios 
mostly greater than 2.8. The assumption that the entire out- 
put would be smelted to high-C ferrochromium would result 
in production of 2.9 million mt of grade A high-C fer- 
rochromium. 

5. Over 75 pet of the evaluated in situ ore tonnage is 
contained in podiform deposits. As in every country where 
most of the chromite resource consists of podiform deposits, 
the lack of podiform deposits of a significant size to allow 
fairly large production levels and reasonable economics for 
underground mining is a constant concern. It is believed 
that the response in Turkey has been the same as in the 
Philippines, in that recent work has been concentrated on 
the location and study of chromite deposits that could be 
mined by large-tonnage surface mining methods. 



Mining and processing losses plus 

nonmetallurgical use products- 

35 pet 




3,096 million mt 

South Africa Minerals Bureau 

estimate, 1980 



"^-^Seam distribution 
\ 



Chromite composition 



Chromite product availability 



FIGURE 7.— Summary of South African cost-evaluated in situ tonnage; percent of total potential, seam distribution, chromite 
composition, and chromite product availability. 



19 



PHILIPPINES 

1. Approximately 11,500 km 2 of area contain outcrops 
of ultramafic complexes and serpentine rocks, which are 
typical host rocks for chromite deposits. 

2. In 1976, a total of 125 chromite deposits or occur- 
rences were listed by the Philippine Bureau of Mines (4). Ap- 
proximately 50 pet were located at Zambales Province, and 
34 pet were located in Mindoro, Palawan, Samar, and 
Dinagat Provinces. 

3. As of 1976, all of the known chromite reserves in the 
Philippines were contained in podiform deposits. Because of 
the endemic problem of limited reserves and resources in 
podiform deposits, a major program was instituted in the 
mid- to late-1970's which emphasized the investigation of 
low-grade eluvial, alluvial, and lateritic chromite deposits. 

4. It was estimated that approximately 6.2 million mt of 
high-Cr chromite products would be available from four ma- 
jor podiform deposits or operations and 5.9 million mt of 
high-Fe chromite products would be available from five ma- 
jor eluvial, alluvial, or lateritic chromite deposits. In addi- 
tion, approximately 4.5 million mt of refractory-grade 
chromite products would be available from two major 
podiform operations. 

5. Because of their small sizes (the vast majority con- 
tained less than 100,000 mt contained ore), the analysis did 
not address the economics of 1.8 million mt of high-Cr 
metallurgical-grade ore contained in 21 podiform deposits 
and 1.1 million mt of refractory-grade ore contained in 12 
podiform deposits. 

6. Because of very low (1.3 to 7.0 pet) Cr 2 3 grades in 
the in situ ore, the low-grade eluvial, alluvial, lateritic 
deposits are presently estimated to be uneconomic, especial- 
ly in relation to the low-cost Finnish and South African pro- 
ducts they would compete with. 



4. It appears that, for internal country usage, any 
chromite product with a Cr-Fe ratio <1.6 will be used for 
chemical production, and any chromite products with a Cr- 
Fe ratio >1.6 will be used for metallurgical purposes. 

5. A total of 81.2 million of in situ ore was estimated to 
represent the demonstrated chromite resources in India, 
with 69.3 million mt in the Cuttack district (including the 
Dhenkenal district) and 9.4 million mt in the Keonjhar 
district -both in Orissa State -and 2.5 million mt at three 
deposits in the Hassan district of Karnataka State. Overall, 
this in situ resource could represent eventual production of 
43 million mt of chromite products, of which 4.9 million mt 
is high-Cr products ( > 2.0 Cr-Fe ratio) and 38.1 million mt is 
high-Fe products for metallurgical and chemical usage. 

6. The foregoing items represent a summary of the find- 
ing in 1980-81. The following items represent recent up- 
dated data that may signify a variance from these data. 

A. The output capacity of the four planned high-C 
ferrochromium smelters will be a combined total of 
200,000 mt/yr. As of 1984, two smelters had been con- 
structed and two were scheduled for completion during 
1985. 

B. Total Orissa State in situ tonnage is 112.6 million 
mt ore with the following indicated characteristics (7): 

65 pet is below a vertical depth of 70 m; much of 
this will require underground mining with possible 
recoveries of only 65 pet. 

Only 23 pet is proven; 66.6 million mt is classified 
as proven and probable. 

Only about 10 pet is lump ore. 

Grade breakdown by usage is 55.0 pet metallurgical 
grade (>48 pet Cr 2 3 , >2.8 Cr-Fe ratio), 32.2 pet 
"charge Cr" grade (42 to 46 pet Cr 2 3 , > 1.6 Cr-Fe 
ratio), and 12.8 pet inferior grade (<40 pet Cr 2 3 , 
< 1.6 Cr-Fe ratio). 



INDIA 

1. In 1975, India's demonstrated resource of in situ 
chromite ore was reported as 17 million mt. Subsequent 
reevaluation of resources by lowering the cutoff grade from 
40 to 30 pet Cr 2 3 resulted in a dramatic increase to 112 
million mt of in situ ore, 60 million mt of which was con- 
sidered as proven (5). All of the additional tonnage is located 
in the Cuttack, Keonjhar, and Dhenkenal districts of Orissa 
State. As a result, in 1980 about 96 pet of the demonstrated 
chromite resource in India was located in Orissa State, with 
only 2 pet in Karnataka State (the Hassan district) and the 
remainder scattered among small deposits in other States. 

2. At the time of the analysis, indications were that 
much of the additional tonnage was probably low-grade (25 
to 35 pet Cr 2 3 ) and high-Fe (1.3 to 1.7 Cr-Fe ratio) material 
represented mainly by the "lower and upper brown" ores of 
the Sukinda Valley (Cuttack and Dhenkenal districts). 
Metallurgical tests have indicated that nearly all of this 
material will require tabling and that some would possibly 
require magnetic separation to produce chromite products 
with Cr-Fe ratios sufficiently high to be used in the new 
"charge" ferrochromium smelters being built in India (6). 

3. A strict tonnage classification of Orissa chromite ores 
into podiform or stratiform deposits is impossible at pres- 
ent; hence, they are classified for this paper as podiform- 
stratiform. Significant tonnages in both types of ore bodies 
are present in the Sukinda Valley and the Keonjhar district, 
although most appears to be in podiform ore bodies. 



BRAZIL 

1. In 1977, chromite resources in Brazil at the inferred 
level were reported as 24 million mt of in situ material (8). 
Of this total, 57 pet was located in the Campo Formosa 
District, 2 pet in the Jacurici Valley, 4 pet in the Alvarado do 
Minas area, and 37 pet in 100 other small deposits scattered 
throughout Brazil. 

2. The analysis of chromite resources resulted in an 
estimated 18.6 million mt of in situ ore at the demonstrated 
level and 39.0 million mt of identified resources. These 
totals included the Campo Formosa District, Jacurici 
Valley, and Alvarado do Minas deposits but did not include 
the 100 other small deposits. 

3. The chromite deposits of the Campo Formosa 
district, which comprised 17.0 million mt of the 
demonstrated and 37.0 million mt of the identified 
resources, are classified as stratiform deposits, while the 
Jacurici Valley and Alvarado do Minas deposits are 
podiform in nature. The additional tonnage for the iden- 
tified level is comprised almost entirely of material that 
would have to be mined by underground methods in the 
Campo Formosa District. 

4. The Campo Formosa District mines account for about 
85 pet of Brazil's current (early 1980's) chromite production. 
The present surface mining operations are characterized by 
very low mill feed grades of 17.0 to 21.0 pet Cr 2 3 , reflect- 
ing high dilution. The Cr-Fe ratios in various products range 
from 1.5 to 2.5. The demonstrated resource in the Campo 



20 



Formosa District would account for about 4.6 million mt of 
chromite products suitable for chemical and metallurgical 
uses, which is just sufficient to supply the country's only fer- 
rochromium smelter at Pojuca. 



FINLAND 

1. The Kemi operations at the north end of the Gulf of 
Bothnia contained the only demonstrated chromite resource 
analyzed. 

2. The surface-minable resource was estimated to be 
29.2 million mt of in situ ore at an average grade of 27.0 pet 
Cr 2 3 and a Cr-Fe ratio of 1.5 to 1.6. This in situ tonnage 
should result in production of 17.0 million mt of high-Fe 
chromite for metallurgical and chemical use and 2.5 million 
mt of chromite concentrates for foundry sand usage. 

3. Surface-minable material was estimated to a max- 
imum depth of 110 m at seven separate ore bodies. There 
could be greater than 30.0 million mt of additional material 
that could be mined by underground methods, but the Kemi 
operation will probably not have to address this aspect for at 
least 25 to 30 yr. 

4. The chromite deposits at Kemi are classified as 
stratiform deposits although they do "pinch and swell" to 
become "lenslike" in places. As much as 85 pet of the ore is 
classified as a "soft, talcose" ore and 15 pet as a "hard, 
serpentinite" ore (.9). 

5. The surface-minable chromite resource at Kemi is a 
very low cost source of high-Fe chromite products. As of 
1980, about 25 pet of the ore and concentrate products were 
required for the nearby ferrochromium smelter at Tornio. 
Usage of Kemi output as feed for the Tornio smelter could 
double, depending upon company plans. The remainder of 
Kemi's output is exported overseas; the Vargon fer- 
rochromium smelter in Sweden is believed to take a fair 
amount of the exports. 

NEW CALEDONIA 

1. About 8,000 km 2 of the country's surface area is 
covered by ultramafic rocks. The entire country contains at 
least 50 individual podiform chromite deposits in 12 
separate ultramafic "massifs" (10). 

2. As of 1980, 82.8 pet of all of New Caledonia's past 
chromite production had come from the Tiebaghi Massif 
(10). The demonstrated resource of chromite ore in the 
Tiebaghi and Fantouche "pipelike" deposits, which provided 
nearly all of this past production, was the only 
demonstrated resource analyzed. 

3. It was estimated that at least 2.3 million mt of in situ 
ore were available in the Tiebaghi and Fantouche pipes for 
underground mining. This resource could result in produc- 
tion of 1.7 million mt of high-Cr chromite products with Cr- 
Fe ratios of 3.0 to 3.6. All production is expected to be ex- 
ported. 



GREECE 

1. Of 12 ultramafic rock complexes in Greece containing 
chromite deposits, only 4 are of large proportions. 
Metallurgical-grade ores are associated with the ultramafic 
complexes in the northern portion of Greece, while 
refractory -grade chromite ores are typically associated with 
the ultramafic complexes in the central portion (11). 

2. Nearly all of the metallurgical chromite production in 
the past has come from the deposits in the Xerolivado 
(Skoumsta) and Voidolakkos areas, which are both located 
in the Mount Vourinos ultramafic complex. 

3. The demonstrated resources analyzed represent the 
tonnage present in the Xerolivado (Skoumsta) mining area 
only. The total in situ tonnage of 2.2 million mt at 18.0 pet 
Cr 2 3 is a podiform resource that should result in the pro- 
duction of 590,000 mt of high-Cr products at a Cr-Fe ratio of 
around 3.0. 

4. The estimated output from Xerolivado (Skoumsta) 
alone would only provide about two-thirds of the feed re- 
quirements for the new high-C ferrochromium smelter 
located at Almyros. Indications are that the Anexitika, 
Koursoumia, and Kersitsa deposits of the Mount Vourinos 
complex would probably provide the additional tonnage 
needed for the Almyros smelter to produce 30,000 mt/yr of 
high-C ferrochromium. 



MADAGASCAR 

1. Chromite deposits occur in three major districts (An- 
driamenha, Befandriana, and Ranomena), all located in the 
northern half of the country. All deposits are podiform in 
nature (mostly lenses) and are mined by surface methods. 
The deposits in the Andriamenha and Befandriana districts 
are high-Cr deposits with Cr-Fe ratios of 2.4 to 3.3. The 
Ranomena district deposits are high-Fe chromite deposits 
with Cr-Fe ratios of 1.3 to 1.5. 

2. Chromite ores from the Ranomena district were only 
produced from 1960 to 1964, the Andriamenha district 
began production in 1964, and deposits in the Befandriana 
district were brought into production in 1975. As of 1980, 
the Andriamenha district was accounting for about 70 pet of 
production and the Befandriana district for 30 pet. Expecta- 
tions were that by 1984 the Andriamenha district would be 
the sole producer. This district has accounted for about 95 
pet of all past chromite production in Madagascar. 

3. Demonstrated resources consisted of 10.0 million mt 
of ore at 31.4 pet Cr 2 3 for the Andriamenha district, 
250,000 mt of ore at 37.0 pet Cr 2 3 at the Ranomena 
district, and 100,000 mt of 45.0 pet Cr 2 3 ore in the Befand- 
riana district. This tonnage could result in production of 3.8 
million mt of high-Cr chromite products and 100,000 mt of 
high-Fe chromite products. 

4. As many as 300 individual deposits have been iden- 
tified in the Andriamenha district (12). The 10.0 million mt 



21 



of ore estimated to be present in the Andriamenha district 
consists of 4.5 million mt at the Ankazatoalana deposit, 1.0 
million mt at the Bemanevika deposit, and an estimated 4.5 
million mt contained in 25 of the other large lens deposits. 



5. There has never been a ferrochromium smelter in 
Madagascar, although studies on construction of a smelter 
were conducted in the mid-1970's and in the early 1980's. 



REFERENCES 



1. Thomas, P. R., and E. H. Boyle, Jr. Chromium 
Availability -Market Economy Countries. A Minerals Availability 
Program Appraisal. BuMines IC 8977, 1984, 86 pp. 

2. Ethem, M. Y. Turkish Chromite: Deposits, Geology and 
Operations. World Min., Sept. 1979, pp. 73-75. 

3. Mineral Research and Exploration Institute of Turkey 
(Ankara). Chromite Deposits of Turkey. MTA Publ. 132, 1966, 108 
pp. 

4. Bacuta, J. C, Jr. Geology of Some Alpine-Type Chromite 
Deposits in the Philippines. Philippine Bur. Mines, Manila, 1978, 20 
pp. 

5. U.S. Embassy, New Delhi, India. State Dep. Airgram A-49 
Attachment, Jan. 14, 1981, pp. 12-14. 

6. Narasimhan, K. S., R. K. Sahoo, and K. L. Narayana. Utility 
of Low Grade Chromites of the Eastern Region. Indian Min. and 
Eng. J., v. 19, No. 6, 1980, pp. 11-18. 

7. Rao, P. M. Minerals Facts and Problems: Chromite. Indian 
Bur. Mines, Min. Res. and Publ. Div., Monog. 6, Mar. 1982, 192 pp. 



8. Ministry of Mines and Energy, Brazil. Anuario Mineral 
Brasiliero (Brazilian Yearbook). Dep. Nac. Prod. Mines. (DNPM), 
Brasilia, v. 5, 1976, p. 169. 

9. World Mining. Mining and Processing Very Low Grade 
Chromite in Finland. Oct. 1974, pp. 54-56. 

10. Cassard, D., A. Nicolas, M. Rabinovitch, J. Montte, M. 
Leblanc and A. Prinzhofer. Structural Classification of Chromite 
Pods in Southern New Caledonia. Econ. Geol., v. 76, 1981, pp. 
805-831. 

11. Zachos, K. The Chromite Mineralization of the Vourinos 
Ophiolitic Complex, Northern Greece. Paper in Magmatic Ore 
Deposits, ed. by H. D. B. Wilson (Proc, Magmatic Ore Deposits 
Symp.). Econ. Geol., Monogr. 4, Lancaster Press, Inc., Lancaster, 
PA, 1969, pp. 147-153. 

12. Besairie, H. Gites Mineraux de Madagascar (Mineral 
Deposits of Madagascar). Bur. Rech. Geol. et Min., Madagascar, 
1968, pp. 118-120. 



BuMines IC 9087: Chromium-Chromite: Bureau of Mines Assessment and Research 



23 



CHROMITE RESOURCES IN ALASKA 

By Jeffrey Y. Foley, 1 James C. Barker, 2 and Lawrence L. Brown 3 



ABSTRACT 



The Bureau of Mines investigated chromite deposits and 
occurrences in Alaska between 1979 and 1984 as part of the 
Bureau's critical and strategic minerals program. Chromite- 
bearing ultramafic rocks are known to occur in 8 regions in 
Alaska; 132 subeconomic podiform-type deposits and 1 
placer deposit are estimated to contain 3.4 million to 4.3 
million st chromic oxide (Cr 2 3 ) in high-Cr and high-Fe 
chromite. Most of the deposits contain between 5 and 10 pet 
chromite, and minesite beneficiation would be required to 
produce shipping-grade concentrates. In the Chugach trend, 
an inferred reserve base comprises 2.8 million st Cr 2 3 in 42 
deposits that are all within 10 miles of tidewater or existing 



transportation routes. Most of these reserves are contained 
in the Turner stringer zone (1.25 million st) and Windy 
River placer deposit (556,000 st) at Red Mountain on Kenai 
Peninsula and in the Halibut Bay complex on Kodiak Island 
(201,000 st). Seventy less accessible deposits in the remote 
western Brooks Range contain between 576,000 and 1.4 
million st high-Cr chromite. The Rampart, Yukon-Koyukuk, 
and Southeast regions contain deposits with minor produc- 
tion potential. No resource estimates are available for 
deposits in the Yukon-Tanana, Alaska Range, and 
Southwest regions. 



INTRODUCTION 



In Alaska, 132 exposed subeconomic podiform-type 
deposits and 1 placer deposit are estimated to contain from 
3.4 to 4.3 million st of chromic oxide (Cr 2 3 ), mostly in high- 
Cr chromite. Based on 1983 consumption statistics, these 
supplies are adequate to satisfy total domestic chromium 
demands for between 9 and 12 yr (16). 

These estimates are based on published descriptions of 
deposits in eight regions, information released to the 
Bureau of Mines by industry, and on-site examination of 
deposits by the Bureau. These estimates include only known 
deposits containing greater than 1,000 st Cr 2 3 and are con- 
sidered conservative. Additional unmeasured resources are 
present in deposits of unknown size. Potential also exists for 
additional exposed and buried deposits in each of the eight 
regions, which have not been completely explored. 

Although small high-grade deposits exist, most 
chromite in Alaska is found in low-grade zones that contain 
between 5 and 10 pet chromite. These low-grade zones con- 
sist of numerous bands of disseminated, coalescent, and 
massive chromite that alternate with nearly barren dunite 



1 Physical scientist, Alaska Field Operations Center, Bureau of Mines, 905 
Koyukuk Ave., North, Fairbanks, AK 99701. 

2 Supervisory physical scientist, Alaska Field Operations Center. 

3 Group supervisor, geologist, Albany Research Center, Bureau of Mines, 
PO Box 70, Albany, OR 97321. 



and peridotite layers. Recovery of chromite from the low- 
grade zones would require mine-site concentration in most 
cases. Metallurgical tests by the Bureau's Albany Research 
Center indicate that much of the chromite in Alaska is of 
high quality and that high-Cr concentrates suitable for 
metallurgical use may be produced. 

Access to chromite deposits in Alaska and land status 
range from practicable to prohibitive. From 65 to 80 pet of 
the estimated reserves are within 10 miles of tidewater or 
existing roads and are on lands open to mineral develop- 
ment. Other deposits are inaccessible except, by airplane, 
and some are in areas such as National Parks that are closed 
to mineral development. These factors must be considered 
in assessing the mineral development potential of a given 
area. 





Abbreviations Used in This Paper 


ft 


foot 


mi 2 
pet 

st 


square mile 
weight percent 
short ton 


yr 


year 



24 



CHROMITE-BEARING REGIONS 



Chromite-bearing ultramafic rocks are concentrated in 
eight larger regions (fig. 1) that are variably defined on the 
basis of geology, geography, and physiography. Of these 
regions, several are appropriately called trends because 
they parallel mountain ranges, major faults, and related 
geologic features. Other, less well-defined regions contain 
scattered chromite-bearing ultramafic bodies that are of 
uncertain relation to one another. The only potentially 
significant lode chromite deposits in Alaska are found in the 
ultramafic portions of alpine peridotite and alpine 
peridotite-gabbro complexes. Many of these complexes are 
associated with pillow basalt, diabase, and chert and are 
therefore interpreted as ophiolite fragments that are ero- 
sional remnants of ocenaic crust that were tectonically 
emplaced along the magrins- of accreting continental crust. 
The chromite-bearing peridotite bodies range from less than 
1 mi 2 to almost 100 mi 2 in area, but most are smaller than 10 
mi 2 . 

Chromite also occurs in minor amounts in zoned 
ultramafic and other igneous complexes that were intruded 
into the earth's crust. Many of these are found in southeast 
Alaska, and one is known in southwest Alaska. More rarely, 
chromite occurs in igneous rocks of mafic to intermediate 
composition such as monzonite and alkali gabbro. 



In the alpine peridotite and zoned ultramafic complexes, 
chromite occurs as disseminated grains and as magmatic 
segregations. The magmatic segregations form layers, 
lenses, irregularly shaped masses, and nodular aggregates 
in dunite and peridotite that are generally referred to as 
podiform-type deposits. Often, parallel layers from less than 
1 inch to several feet wide are concentrated in zones that 
measure tens, hundreds, or even thousands of feet in area 
and thickness. The largest known deposit of this type is the 
Turner stringer zone at Red Mountain on Kenai Peninsula. 

Chromite is also concentrated in placer deposits on 
beaches and in alluvial deposits that are proximal to 
chromite-bearing rocks, but little exploration has been done 
for placer chromite in Alaska. Most reported placer 
chromite occurrences, however, consist of accessory to 
minor chromite in highly concentrated black sands {2-U) that 
were produced during placer gold mining operations or sedi- 
ment sampling where very little ultramafic rock is known, 
and most of the reported placer occurrences are therefore 
not likely to be significant resources. Potential does, 
however, exist for recoverable placer chromite in valleys 
draining some of the areas described in this report. 



Prydhoe Boy 



LEGEND 

Chromite-bearing 
regions 



% 



iP& 




FIGURE 1.— Chromite-bearing regions in Alaska. 



25 



CHUGACH TREND 

Foremost among the chromite-bearing regions in 
Alaska is the Chugach trend from which Alaska's only 
chromite production has come. This trend is a narrow belt 
that parallels the arcuate Border Ranges Fault and the 
Chugach Mountains for over 600 miles in southern Alaska. 
Within this trend, fault-bounded masses of chromite bearing 
alpine peridotite and associated gabbroic rocks are discon- 
tinuously present from near the Canadian Border to Kodiak 
Island (fig. 2). Podiform chromite deposits are present in 
ultarmafic rocks near Tonsina, Palmer, and Eklutna, at Red 
Mountain and Claim Point on Kenai Peninsula, and- in the 
Halibut Bay Complex on Kodiak Island (6-7). About 2.8 
million st of Cr 2 3 in high-Cr chromite is estimated in 41 
hard-rock and 1 placer deposits (table 1) that are all within 
10 miles of tidewater or existing roads (6-7). 

At Bernard Mountain, near Tonsina, 343,000 st of 
Cr 2 3 is estimated in three deposits containing about 5 pet 
chromite each (7). Twelve smaller and higher grade deposits 
are also present. Twenty-six thousand short tons of Cr 2 3 is 



estimated in one deposit at Sheep Hill, about 4 miles east of 
Bernard Mountain. Because of their small size or high-Fe 
content in contained chromian spinels, no tonnages were 
estimated for 11 other occurrences and deposits at Sheep 
Hill and adjacent Dust Mountain. 

Within the Wolverine Complex, near Palmer, are seven 
occurrences for which no tonnage estimates were made. 

TABLE 1.— Summary of chromite deposits along 
the Border Ranges Fault 



Complexes 


Deposits 


Cr 2 0„ 10 3 st 


Tonsina area: 


3 
1 

1 

23 

1 

10 

3 


343 


Sheep Hill 

Palmer area: 

Kenal Peninsula: 


26 

1 
1,575 


Windy River 

Claim Point 


556 
90 


Kodiak Island: 
Halibut Bay area 


201 


Total 


42 


2,792 







ALASKA 



KEY 

Ultramafic rocks and mat ic-ultramafic complexes 

1 - Chakins. Klu. Chitna. and Hanagila Rivers 

2 - Dust Mountain 

3 - Sheep Hill 

4 - Bernard Mountain 

5 - Nelchina 
a - Wolverine 
7 - Eklutna 
S - Red Mountain and Windy Rive 

9 - Claim Point 

10 - Ban Island 

11 * Miners Point 

12 - Karluk 

13 - Saddle Mountain 

14 - Middle Cape 

a. Qurney Bay 

b. Halibut Bay 

c. Sturgeon River 

d. Grant Lagoon 




^» 



Scale, miles 



FIGURE 2.— Chugach trend. 



26 



Most of these occurrences consist of banded and massive 
chromian spinel in talus and morainal debris. Metallurgical 
tests on a bulk sample from the largest occurrence in the 
Wolverine Complex indicate marginal-quality chromite with 
a Cr-Fe ratio of about 1.6 is present. 

Near Eklutna, between Palmer and Anchorage, are six 
chromite occurrences and deposits that were drilled and 
trenched in the 1940's by the Bureau. These deposits are 
small and probably insignificant, but it is likely that addi- 
tional and perhaps more significant deposits there are 
obscured by vegetation so dense that it has already com- 
pletely overgrown the Bureau's earlier excavations. 

Chromite was produced from two areas on Kenai Penin- 
sula: Red Mountain and Claim Point (fig. 2). During the 
First and Second World Wars and the Korean conflict, a 
total of about 30,000 st chromite ore with reported grades 
between 38 and 43 pet Cr 2 3 was produced from the Star 
No. 4 and Chrome Queen Mines at Red Mountain and the 
Reef Mine at Claim Point (7). Of the chromite ore produced 
on Kenai Peninsula, about 8,000 st was shipped to Japan in 
1976. (18). 

A 10-mile road reaches Red Mountain from tidewater 
on Jakolof Bay near the community of Seldovia. Thirty- 
three chromite deposits at Red Mountain have been de- 
scribed by U.S. Geologrical Survey, Bureau of Mines, and 
Anaconda Minerals geologists. Prior to recent Anaconda 
and Bureau investegations, 97,000 st contained Cr 2 3 was 
inferred in 20 deposits that contain 30 pet or more chromite 
(11-12). Based on mapping, drilling, and trenching by 
Anaconda, and metallurgical testing by the Bureau of 
Mines, about 1.5 million additional short tons of Cr 2 3 is 
estimated in three low-grade deposits (1, 6-7). These include 
the Turner, Star, and Horseshoe stringer zones. The Turner 
stringer zone contains 1.25 million st Cr 2 3 at an average 
grade of 5.6 pet Cr 2 3) the Star stringer zone 208,000 st at 
6.9 pet Cr 2 3 , and the Horseshoe stringer zone 29,000 st at 
4.5 pet Cr 2 3 . Three other low-grade deposits, the Tram 
Road, Richards, and Tom stringer zones, remain un- 
evaluated, and no tonnage estimates are presented. 

Of all the chromite deposits in Alaska, those at Red 
Mountain are prehaps the best exposed and certainly the 
most explored. Based on surface sampling, drilling, seismic 
surveys, and metallurgical tests by Anaconda and the 
Bureau, 556,000 st of contained Cr 2 3 is estimated in 
gravels with a grade of 1.3 pet Cr 2 3 in the Windy River 
placer deposit at Red Mountain. 

Ninety thousand short tons of Cr 2 3 is estimated in 8 of 
16 hard-rock chromite deposits that have been described at 
Claim Point, on the southern tip of Kenai Peninsula (fig. 3). 
Over 2,000 st of chromite ore was produced from the Reef 
deposit in the First World War. This deposit contains at 
least 15,000 st Cr 2 3 at grades greater than 40 pet 
chromite. The deposit is largely under water and probably 
contains more chromite than present estimates indicate. 
Banded chromite typical of the Reef deposit is shown in 
figure 4. 

The largest deposit at Claim Point is deposit 10, which 
was trenched and drilled by the Bureau in the 1940's. By 
lowering cutrff grades, indicated reserves for this deposit 
were increased from about 54,000 st to over 71,000 st dur- 
ing recent Bureau investigations. Other smaller deposits at 
Claim Point include low-grade stringer zones and higher 
grade, massive chromite bands such as the one at deposit 2 
(fig. 5). 



Chromite-bearing alpine-peridotite bodies are present 
at several locations on the southwest end of Kodiak Island. 
These include ultramafic bodies near Halibut Bay, Miners 
Point, Grant Lagoon, Gurney Bay, Saddle Mountain, and 
the Sturgeon River. Similar rocks are reported on Ban and 
Afognak Islands. Most occurrences observed by the Bureau 
are small and low grade, but one large deposit, with 5 pet 
chromite, in the Halibut Bay complex is estimated to contain 
196,000 st Cr 2 3 . Two other deposits there contain 5,000 st 
Cr 2 3 combined; no estimates were made for eight other oc- 
currences in the complex. 




FIGURE 3.— Claim Point, Kenai Peninsula. 




FIGURE 4.— Banded chromite in the Reef deposit, Claim Point. 




im. 



FIGURE 5.— Massive chromite band at deposit 2, Claim Point. 



27 



SOUTHEAST TREND 

Minor chromite is reported in ultramafic rocks at 
numerous locations in southeast Alaska (fig. 1). Most of 
these occurrences are in dunite portions of Alaskan-type 
ultramafic complexes that show concentric zoning of rock 
types and are interpreted to be exposed subvolcanic magma 
chambers (14). The only complex in southeast Alaska for 
which resource estimates are available is Red Bluff Bay on 
Baranof Island, where 32,000 st of low-grade material with 
about 12 pet Cr 2 3 is present in eight deposits that comprise 
small lenses, thin layers, and disseminated chromite in 
dunite (IS, 15). 



WESTERN BROOKS RANGE TREND 

The western Brooks Range trend (figs. 1 and 6) in 
northwestern Alaska comprises chromite-bearing 
ultramafic rocks at Iyikrok Mountain, in the Avan Hills, and 
at Misheguk, Siniktanneyak, and Asik Mountains. This 
ophiolite trend extends from the Chukchi Sea to Howard 
Pass, a distance of about 200 miles, and contains between 
576,000 and 1.4 million st Cr 2 3 in 70 high-Cr and high-Fe 
chromite deposits (10). These estimates are based on 
traverses made by four people in a 200 -mi 2 area, during two 




FIGURE 6.— Western Brooks Range trend. 



28 



2- week periods, and additional deposits undoubtedly exist. 
Next to deposits in the Chugach trend, deposits at Iyikrok 
Mountain and in the Avan Hills are prehaps the most likely 
to be developed, as they would be made accessible by a pro- 
posed road from a port site on the Bering Sea coast near 
Kivalina to the Red Dog lead-zinc-silver deposit, where pro- 
duction may begin as early as 1989. Some of the western 
Brooks Range deposits are within the Noatak National 
Preserve, administered by the National Park Service. 



YUKON-KOYUKUK TREND 

The Yukon-Koyukuk basin in northern and central 
Alaska (fig. 1) is bounded on the north and southeast by 
ophiolitic rocks that locally contain high-Cr chromite. 
Podiform-type deposits are present at Caribou Mountain, 
along the Kanuti and Kilolitna Rivers, and near Holonada 
Creek (5, 9). Except for the small deposits at Caribou Moun- 
tain on the Dalton Highway, helicopters provide the only 
practical access to chromite deposits in this region. Except 
for one deposit in the Holonada mass that contains between 
13,000 and 26,000 st Cr 2 3 , exposed deposits in the Yukon- 
Koyukuk trend are estimated to contain less than 1,000 st 
each (10). 



ALASKA RANGE TREND 

Fault-bounded and intrusive masses of alpine peridotite 
and serpentinite of Paleozoic and Mesozoic age crop out at 
numerous locations in a narrow, 400-mile-long trend that 
parallels the Alaska Range from near the Canadian border 
to near Farewell (fig. 1). The origins and relative ages of 
these ultramafic rocks are unknown, but most are elongated 
parallel to the Denali Fault and were possibly emplaced into 
the crust during deformation along the fault. Although the 
Alaska Range is crossed by two highways and a railroad, ac- 
cess to chromite deposits in this trend is limited to 
helicopter travel. 

Chromite is reported in alpine peridotite and serpen- 
tinite masses at several locations in the Alaska Range trend, 
but few of the masses have been thoroughly investigated for 
their chromite potential. No reserve estimates are available. 
Of the reported chromite occurrences in the Alaska Range, 
those near Lacuna and Yentna Glaciers and in the Chulitna 
area have the greatest reserve potential. Chromite is 
reported at several locations in the Lacuna and Yentna 
Glaciers area, where the largest occurrence is an 8-ft by 
60-ft lens of massive, high-Cr chromite (17). Similar, nearly 
massive chromite bands up to 1-ft thick are also present 
near Copeland Creek in the Chulitna area. 



RAMPART TREND 



SOUTHWEST REGION 



Parallel to the southeast limb of the Yukon-Koyukuk 
trend are poorly exposed ophiolitic rocks of the Rampart 
trend (fig. 1), which are offset right-laterally along the 
Kaltag Fault. There are no roads, and access to this region 
is generally difficult. Podiform-type deposits are present in 
the Kaiyuh Hills at the southwest end, and minor chromite 
has been observed in the Christian River mass to the north- 
east. Of 21 occurrences and deposits in the Kaiyuh Hills, 4 
contain between 17,000 and 37,000 st Cr 2 3 (8). 



YUKON-TANANA UPLANDS REGION 

Minor chromite is reported at numerous locations in the 
Yukon-Tanana uplands region (fig. 1), but no significant 
concentrations are known. The region is largely covered by 
unconsolidated surficial deposits and vegetation, and where 
exposed, ultramafic rocks are typically small, extensively 
faulted and altered, and contain only accessory chromite. 
Metallurgical tests by the Bureau of Mines on low-grade 
material from Nail Ridge, one of the larger and better ex- 
posed masses, indicate the chromium spinel there is un- 
suitable for industrial use. 



The southwest region includes chromite-bearing alpine 
peridotite and alpine peridotite-gabbro masses of varied 
origin and ages at Mount Hurst, Tatlignagpeke Mountain, 
Mitlak Mountain, Red Mountain, and Susie Mountain, and 
chromite-bearing monzonite near Moore Creek and Fourth 
of July Creek (fig.). This region extends southwest from 
Mount Hurst, near Tolstoi, to Goodnews Bay, a distance of 
about 450 miles. Deposits in this region are some of the 
most remote in the State. Ultramafic rocks at Mount Hurst 
may be related to ultramafic and related rocks in the Kaiyuh 
Hills, 75 miles to the north, which are in the Rampart 
ophiolite belt. Tatlignagpeke Mountain and Mitlak Moun- 
tain, between the Arolik and Goodnews Rivers, consist of 
serpentinized, strongly tectonized, and layered peridotite 
and gabbroic rocks that structurally overlie Mesozoic and 
Paleozoic sedimentary and volcanic rocks. At Goodnews 
Bay, an Alaskan-type ultramafic complex with accessory 
chromite is the source of platinum-group metals in the 
Salmon River placer deposit. Small chromite-bearing mon- 
zonite plutons are intruded into sedimentary rocks of the 
Cretaceous Kuskokwim Group near Moore Creek and 
Fourth of July Creek. No reserves are estimated for any of 
the southwest chromite occurrences. 



29 



SUMMARY 



Estimates of Cr contained in Alaskan deposits are sum- 
marized in table 2. Most of these estimates are based on sur- 
face observations made during examination of the chromite- 
bearing masses; additional reserves probably exist in un- 
discovered buried deposits, covered extensions of known 
deposits, and placer deposits in streams adjacent to the 
chromite-bearing masses. The deposits occur within eight 
geographic or geologic regions. The podiform-type deposits 
range in size from a few tons to over 1 million st of con- 
tained Cr 2 3 . The total estimated reserve potential is 3.4 
million to 4.3 million st contained Cr 2 3 and is sufficient to 
satisfy total domestic Cr demands for 9 to 12 yr. These ton- 
nages are mostly contained in low-grade deposits with less 
than 10 pet chromite. Mine site beneficiation of the chromite 
would be required to produce shipping-grade concentrates. 
Metallurgical tests and geochemical analyses on samples 
from most of these deposits indicate that high-Cr concen- 
trates can be recovered. 

Only the Chugach trend contains deposits that are large 
enough (2.8 million st Cr 2 3 in 42 low-grade deposits) and 
close enough to tidewater or existing transportation routes 
to significantly offset chromium shortages in the event of an 
interruption of foreign supplies. 



Seventy low-grade deposits in the remote Western 
Brooks Range trend contain an estimated 576,000 to 1.4 
million st Cr 2 3 . Most of the Western Brooks Range 
deposits will become more accessible when the proposed 
road to the Red Dog lead-zinc-silver deposit is constructed. 

TABLE 2.— Summary of chromite deposits In Alaska 





Number of 
deposits' 


Contained Cr 2 3 , 
10 3 st 


Region 


Type 1 


Type 2 


Western Brooks Range 

trend 

Yukon-Koyukuk trend .... 

Rampart trend 

Yukon-Tanana uplands 


70 
9 
4 




42 
8 


>100 

>50 

20 

>5 
>15 
>30 
>94 
>22 


576-1,394 
17- 31 
17- 37 




Alaska Range trend 

Southwest region 

Chugach trend 

Southeast region 






2,800 

4 


Total 


133 


>336 


3,414-4,266 



'Type 1 includes only deposits for which estimated reserves or 
estimated reserve potential is inferred. Type 2 comprises identified 
deposits and occurrences, including those for which no reserve estimates 
are available. 



REFERENCES 



1. Anaconda Minerals Co. 1981 Annual Report on Red Mountain. 
Anchorage, AK, 1981, 43 pp.; available upon request from J. Y. 
Foley BuMines, Fairbanks, AK. 

2. Cobb, E.H. Chromite Occurrences in Alaska. U.S. Geol. Surv. 
Map MR-68, 1975: scale 1:2,500,000. 

3 . Placer Deposits of Alaska. U.S. Geol. Surv. Bull. 1374, 

1973, 213 pp. 

4. Cobb, E.H., and D.R. St. Aubin. Occurrences of Selected 
Critical and Strategic Mineral Commodities in Alaska. U.S. Geol. 
Surv. OFR 82-719, 1982, 24 pp. 

5. Dahlin, D.C., L.L. Brown, and J.J. Kinney. Podiform Chromite 
Occurrences in the Caribou Mountain and Lower Kanuti River 
Areas, Central Alaska, Part II: Beneficiation. BuMines IC 8916, 
1983, 15 pp. 

6. Dahlin, D.C., D.E. Kirby, and L.L. Brown. Chromite Deposits 
Along the Border Ranges Fault, Southern Alaska, Part II: Bene- 
ficiation. BuMines IC 8991, 1984, 37 pp. 

7. Foley, J.Y., and J.C. Barker. Chromite Deposits Along the 
Border Ranges Fault, Southern Alaska. Part I: Field Investigations 
and Descriptions of Chromite Deposits. BuMines IC 8990, 1984, 57 
pp. 

8. Foley, J.Y., T. Hinderman, D.E. Kirby, and C.L. Mardock. 
Chromite Occurrences in the Kaiyuh Hills, West-Central Alaska. 
BuMines OFR 178-84, 1984, 20 pp. 

9. Foley, J.Y., and M.M. MeDermott. Podiform Chromite Occur- 
rences in the Caribou Mountain and Lower Kanuti River Areas, 



Central Alaska, Part I: Reconnaissance Investigations. BuMines IC 
8915, 1983, 27 pp. 

10. Foley, J.Y., J.C. Barker, and L.L. Brown. Critical and 
Strategic Minerals Investigations in Alaska: Chromium. BuMines 
OFR 97-85, 1985, 54 pp. 

11. Gill, A.C. Chromite of Kenai Peninsula, Alaska. U.S. Geol. 
Surv. Bull. 742, 1922, 52 pp. 

12. Guild, P.W. Chromite Deposits of Kenai Peninsula, Alaska. 
U.S. Geol. Surv. Bull. 931-G, 1942, pp. 139-176. 

13. Guild, P.W., and J.R. Balsley, Jr. Chromite Deposits of Red 
Bluff Bay and Vicinity, Baranof Island, Alaska. U.S. Geol. Surv. 
Bull. 936-G, 1942, pp. 171-187. 

14. Irvine, T.N. Petrology of the Duke Island Ultramafic Com- 
plex, Southeastern Alaska. Geol. Soc. Am. Memoir 138, 1974, 240 
pp. 

15. Kennedy, G.C., and M.S. Walton, Jr. Geology and Associated 
Mineral Deposits of Some Ultrabasic Rock Bodies in Southeastern 
Alaska. U.S. Geol. Surv. Bull. 947-D, 1946, pp. 65-84. 

16. Papp, J.F. Chromium. BuMines Mineral Commodity Profile, 
1985, 17 pp. 

17. Reed, B.L., S.W. Nelson, G.C. Curtain, and D.A. Singer. 
Mineral Resources Map of the Talkeetna Quadrangle, Alaska. U.S. 
Geol. Surv. Misc. Field Studies Map MF 870-D, 1978; scale 
1:250,000. 

18. Service, A.L. The Mineral Industry in Alaska. Ch. in BuMines 
Minerals Yearbook, 1976, v. 2, pp. 59-76. 



BuMines IC 9087: Chromium-Chromite: Bureau of Mines Assessment and Research 



31 



CHROMIUM RESOURCES IN THE CONTERMINOUS UNITED STATES 

By Nicholas Wetzel 1 
ABSTRACT 



The Bureau of Mines is evaluating Cr resources in the 
conterminous United States (suitable for both metallurgical 
and chemical use) for Cr availability by State, county, 
deposit, and operation. The investigation to date has iden- 
tified more potential resources than previously believed to 
be present. 

Low-Fe Cr resources (Cr-Fe ratios > 2.0) are estimated 
at 1.6 million mt Cr 2 3 contained in 14.6 million mt of 
chromite-bearing material in California (95 pet), Oregon (4.5 
pet), and Washington (0.5 pet) podiform deposits. High-Fe 
resources (Cr-Fe ratios of 1.5 to 2.0) are estimated at 12.4 



million mt Cr 2 3 contained in 138.5 million mt of chromite- 
bearing material in Montana (75.5 pet), California (20 pet), 
Oregon (3.7 pet), Wyoming (0.7 pet), and the Appalachian 
region (<0.1 pet). 

Additional resources with excessively high Fe contents 
(Cr-Fe ratios < 1.5) that may be a potential Cr source in the 
future total 7.6 million mt Cr 2 3 contained in 448.5 million 
mt of chromite-bearing material in Oregon beach sands and 
laterites (57 pet), California laterites and asbestos proper- 
ties (40 pet), Washington iron deposits (3 pet), and Montana 
podiform deposits (<0.1 pet). 



INTRODUCTION 



The objective of this report is to estimate the quantity 
and quality of identified domestic Cr resources 2 present in 
the conterminous 48 States. For purposes of this study, 
domestic resources have been classified into two categories 
based on Fe content: low-Fe and high-Fe. These categories 
roughly parallel the distinction between metallurgical and 
chemical grades; however, owing to the increasing inter- 
changeability among grades, a dollar value per metric ton of 
product is more applicable. "Low-Fe" chromites comprise 
ores and concentrates similar in product grade to those pro- 
duced in Turkey that have a Cr-Fe ratio near 3.0 and are 
estimated to be valued at $110/mt. "High-Fe" chromites 
comprise ores and concentrates similar in product grade to 
those produced in South Africa that have Cr-Fe ratios rang- 
ing from 1.5 to slightly over 2.0 and are estimated to be 
valued at $52/mt. 

To date, total domestic production has been < 2 million 
mt of lump ore and concentrates averaging 41.1 pet Cr 2 3 
with an average Cr-Fe ratio of 2.0. Of this total, 30 pet was 
low-Fe material derived solely from podiform deposits in 
California and Oregon (table 1). The remaining production 
was of the high-Fe variety, the bulk of which came from the 
Stillwater Complex in Montana (70 pet) or podiform 
deposits in Pennsylvania and Maryland (19 pet). The balance 
of high-Fe chromites came from podiform or beach sand 
deposits in Oregon (7 pet) and California (4 pet) (table 2). 



' Physical scientist, Western Field Operations Center. Bureau of Mines. 
East 360 Third Ave.. Spokane, WA 99202. 

2 Identified resources- Resources whose location, grade, quality, and 
quantity are known or estimated from specific geologic evidence; include 
economic, marginally economic, and subeconomic components. 



Domestic resources are contained in four types of 
deposits: (1) podiform, (2) stratiform, (3) lateritic soil, and 
(4) placer. 

Podiform deposits are associated with alpine-type 
peridotite bodies in California, Oregon, and Washington 
that have been tectonically emplaced from marginal basins 
over areas of active island-arc volcanism. Typically, these 
peridotites are approximately 95 pet harzburgite, with the 
remaining 5 pet composed of scattered patches of dunite 
and irregular seams of orthopyroxenite. Dunite and 
chromite normally occur together in harzburgite, with 
chromite usually found in the dunite or its most common 
alteration product, serpentine. The dunite typically occurs 
as irregular patches, tabular lenses, or pods ranging from a 
few cubic meters to thousands of cubic meters. 

Stratiform deposits of the Stillwater Complex are con- 
tained in a large layered igneous intrusive. Chromite 





Abbreviations Used in This Paper 


ft 


foot 


in 


inch 


km 


kilometer 


m 


meter 


mt 


metric ton 


pet 


weight percent 


yr 


year 



32 



TABLE 1.— Production by type and quality ' 



Type 



Ore 
shipped, mt 



Cr 2 0„ 
pet 



Cr-Fe 
ratio 



Contained 
Cr,0,, mt 



Source, 
State and pet 



LOW-Fe 



Podiform: 

Disseminated 

Massive 


242,300 
333,100 


45.5 
46.5 


2.6 
2.9 


110,300 
154,900 


94 CA, 6 OR. 
85 CA, 15 OR. 


Total 


575,400 


46.1 


2.8 


265,200 


89 CA, 11 OR. 



HIGH-Fe 



Podiform: 












Disseminated 


70,300 


42.4 


2.0 


29,800 


51 CA, 28 OR, 21 MT. 


Massive 


280,600 


39.8 


1.6 


111,600 


84 MD-PA, 2 10 OR, 6 CA. 


Stratiform 


954,600 


38.6 


1.6 


368,500 


100 MT. 


Placers 


68,600 


39.5 


1.5 


27,100 


70 OR, 30 MD-PA. 


Total 


1,374,100 


39.1 


1.6 


537,000 


70 MT, 7 OR, 19 MD-PA, 4 CA. 



1 Production reported in this table is considered conservative. Where detailed production data were not available or the records appeared 
duplicative, minimum figures are used. 

2 All production from Maryland and Pennsylvania podiform deposits occurred prior to 1900 (16). 
Sources: References 2-4, 6, 16, 20, 23-24, 33, 35-37. 



minerals and enclosing harzburgite originally formed in 
horizontal layers as a cumulate or "magmatic sediment" dur- 
ing fractionation of a basaltic magma (U). 

Lateritic soil deposits occur in the northern California- 
southern Oregon coastal region and are derived from 
weathering of alpine peridotites which host podiform 
chromite deposits. Chromite concentrations rarely exceed 3 
pet Cr 2 3 . 

Placer deposits occur along the southern coast of 
Oregon where black sands were concentrated by wave ac- 
tion and currents and deposited along former coastlines ad- 
jacent to the cliffs and in offshore depressions (8). 



TABLE 2.— Production and resources by State 



State 



Montana 

California 

Oregon 

Washington . . . 

Wyoming 

Maryland 

Pennsylvania . . 
North Carolina 
Georgia 



Contained Cr,0,, mt 



Production 



375,900 

257,500 

66,800 





1 102,000 






' All prior to 1900. 



Resources 



9,464,600 

6,910,100 

4,817,100 

252,400 

92,500 

( 7,300 

6,300 

3,500 

600 



OVERVIEW 



Low-Fe chromite resources in the conterminous United 
States are estimated at 1.6 million mt contained Cr 2 3 in 
14.6 million mt of chromite-bearing material (table 3). Over 



99 pet of these resources are contained in podiform deposits 
of California and Oregon (fig. 1). Within these deposits over 
97 pet of the resource is contained within the larger 



TABLE 3.— Resources by type and quality 



Type 



Ore, mt 



Cr,0„ 
pet 



Cr-Fe 
ratio 



Contained 
CrjO,, mt 



Source, 
State and pet 



LOW-Fe 



Podiform: 

Disseminated 

Massive 


14,422,600 
189,000 


10.2 
42.9 


2.5 
2.9 


1,474,000 
81,000 


95.0 CA, 4.0 OR, 1.0 WA. 
76.0 CA, 24.0 OR. 


Total 


14,611,600 


10.6 


2.5 


1,555,000 


95.0 CA, 4.5 OR, .5 WA. 



Stratiform 

Placer: 

Beach sands 

Placer 

Podiform: 

Disseminated 

Massive 


46,215,900 

8,768,700 
1,247,700 

82,040,700 
188,500 


20.6 

4.9 
1.4 

3.0 
22.6 


1.6 

1.4 
1.5 

2.0 
2.0 


9,514,200 

433,500 
17,700 

2,420,200 
42,500 


98.9 MT, 1.1 WY. 

88.7 OR, 11.3 CA. 
41.2 MD, 35.6 PA. 

19.8 NC, 3.4 GA. 

98.5 CA, 1.5 MT. 
100.0 OR. 


Total 


138,461,500 


9.0 


1.8 


12,428,000 


75.5 MT, 20.0 CA, 
3.7 OR, .7 WY, 
.1 others 



POTENTIAL SOURCES 



Laterltes 


200,000,000 

196,819,000 

41,058,000 

10,591,300 

18,000 


1.0 
2.6 

.7 

2.1 

30.0 


NAp 
NAp 
NAp 
.6 
1.1 


2,000,000 

5,073,000 

271,000 

221,700 

5,400 


100.0 OR. 

54.0 CA, 46.0 OR. 

100 CA 


Iron ore 

Podiform 


100.0 WA. 
100.0 MT. 


Total 


448,486,300 


1.7 


1.0 


7,571,100 


57.2 OR, 39.8 CA, 
2.9 WA, .1 MT. 



NAp Not applicable. 



33 




EXPLANATION 
Contained Cr^O^, mt 
Low-Fe 
OLen than 100,000 
• 100,000 to 1,000,000 

High-Fe 
A Less than 100,000 
A 100,000 to 1,000,000 
A More than 1,000,000 



1. Stillwater Complex 

2. SW Oregon Beach Sands 

3. Pilliken Area 

4. CA-OR Laterites 

5. Seiad Creek Area 

6. Hamburg-McGuffy Creek Area 

7. Bar Rick Mine 

8. Broken Ladder Area 

9. Coggins Mine 

10. Little Castle Creek Mine 

1 1. North Elder Creek Area 



12. 


Grey Eagle-Black Diamond Area 


23. 


Cle Elum Deposit 


13. 


Lambert Mine 


24. 


Blewett Pass Deposit 


14. 


McCormick Mine 


25. 


Twin Sisters Area 


15. 


Long Ledge-Jack Sprat Area 


26. 


Table Mountain Prospect 


16. 


Butler Estate 


27. 


Red Lodge Area 


17. 


San Luis Obispo County Area 


28. 


Casper Mountain Deposit 


18. 


San Benito-Tulare-Fresno Asbestos 


29. 


State Line District 


19. 


Crescent City Beach Sands 


30. 


Morgan Hill-Lancaster-Holcombe Deposits 


20. 


Sourdough Area 


31. 


Louise Deposits 


21. 


Chrome Ridge Area 






22. 


John Day Area 







FIGURE 1.— Location of significant chromite deposits in the conterminous United States. 



disseminated deposits grading from 5 to 20 pet Cr 2 3 rather 
than the small scattered pods of shipping-grade ore. 

High-Fe chromite resources are estimated at 12.4 
million mt contained Cr 2 3 in 138.5 million mt of chromite- 
bearing material. Of this total, 75 pet is contained in 
stratiform deposits of the Stillwater Complex, 21 pet in 
disseminated podiform deposits of California, and 3 pet in 
beach sand deposits of southwest Oregon. Less than 1 pet is 
contained in stratiform deposits of Wyoming, disseminated 
deposits of Montana, or alluvial deposits of Pennsylvania, 
Maryland, Georgia, and North Carolina. 



Additional chromite resources are available from lower 
grade beach sand deposits in southern Oregon and as poten- 
tial byproducts from laterites, asbestos deposits, and iron 
ore deposits. These resources contain nearly 7.6 million mt 
Cr 2 3 in 448.5 million mt of material. Over 67 pet of this 
resource is contained in laterite deposits of California and 
Oregon, 26 pet in southwest Oregon beach sands, 3.5 pet in 
asbestos properties in California, 3.1 pet in Washington iron 
ore deposits, and < 0.1 pet in exceedingly high-Fe podiform 
deposits in Montana. 



MONTANA 



Montana's estimated resources are 42.9 million mt ore 
containing 9.5 million mt Cr 2 3 . More than 99 pet of this 
total is in stratiform deposits of the Stillwater Complex. The 
remaining resource occurs in several small massive and 
disseminated podiform deposits in the Red Lodge District, 
some 50 km southeast of the Stillwater Complex, and the 
Table Mountain asbestos prospect in the Spanish Peaks 
Primitive Area, approximately 100 km west of the 
Stillwater Complex. All chromite resources in Montana are 
high in Fe, with Cr-Fe ratios averaging 1.6. 



STILLWATER COMPLEX 

The Stillwater Complex, a large layered intrusive body, 
lies along the northern margin of the Beartooth Mountains 
and is exposed along a strike length of 45 km; exposed width 
ranges between 3 and 6 km. The 2.9-billion-year-old Ar- 
chean Age complex intrudes even older metasediments to 
the south and is uncomformably overlain by Middle Cam- 
brian sediments to the north. The complex, for classification 
purposes, has been divided into three zones, the Basal, 



34 



Ultramafic, and Banded Zones (30). Chromite is concen- 
trated in 13 separate, alphabetically designated (oldest to 
youngest) chromitite layers within olivine-rich rocks of the 
Ultramafic Zone in the lower part of the complex (13). In- 
dividual layers are not omnipresent; only two, the G and H 
layers, are believed to contain potential chromite resources. 
All significant occurrences are associated with poikilitic 
rock of harzburgite composition. 

Chromite was first noted in the vicinity of the present 
Benbow Mine in 1918. From 1918 to 1929, Chromium Prod- 
ucts Corp. made several unsuccessful attempts to develop 
the property. In 1939, the Bureau of Mines began a 6-yr 
study which included trenching, drilling, and channel sampl- 
ing of the G chromitite layer. During this study, a Canadian 
firm acquired the Benbow property and drove a 425-m ex- 
ploration adit. When the Canadian firm relinquished its in- 
terests, the Anaconda Co., under Government contract to 
supply concentrates, initiated development. From 1941 to 
1943, Anaconda developed 14,261 m of underground work- 
ings and completed 804 m of diamond drilling to define, in 
part, the resources of the G chromitite layer (31). During the 
3-yr production period, Anaconda mined 203,844 mt ore at 
an average grade of 18.4 pet Cr 2 3 . About 169,000 mt of 
this total was processed at the Benbow mill to yield 65,832 
mt of 41.5-pct-Cr z 3 concentrate. 

The Mountain View chromite deposit was discovered 
and claimed in stages between 1880 and 1918. Development 
continued sporadically from 1918 to 1930; however, no 
significant production occurred until the Government con- 
tract was let to the Anaconda Co. in 1941. Anaconda com- 
pleted about 12,000 m of underground development from 
1941 to 1943. The mill processed 70,485 mt of 19.3-pct- 
Cr 2 3 ore to produce 26,796 mt of 38.8-pct-Cr 2 3 concen- 
trate. An additional 95,711 mt was mined and stockpiled. 

The American Chrome Co., also under Government con- 
tract, reopened the Mountain View Mine in 1953. From 
1953 to 1961, 18,832 m of development work was com- 
pleted. During the 8-yr period of operation, 862,000 mt of 
38.6-pct-Cr 2 3 concentrate was produced. In 1958, a pilot 
ferrochromium plant was constructed that yielded promis- 
ing test results (31). 

The Gish property, located in 1918, was not developed 
until 1942 when Anaconda, under Government contract, 
completed 1,239 m of underground workings. None of the 
mined ore was milled. 

The Nye Basin area was explored by trenching and dia- 
mond drilling by the Bureau during the 1930's and 1940's. 
No subsequent exploration has taken place. 

The stockpile produced by American Chrome was com- 
pleted at a cost to the Government of $33/mt. In 1974, the 
stockpile was sold to Metallurg Inc. of New York, at a 
reported sale price of $9/mt. In 1975, approximately half of 
the stockpile was hauled by truck to Columbus, MT, then 
shipped by rail to Great Lakes ports; some of the concen- 
trate was subsequently shipped to Germany, Sweden, and 
the United States. Truck haulage was terminated in 1975 
because of road damage. In the summer of 1982 truck 
haulage was resumed, and the remaining concentrates were 
moved to Columbus, MT. 



Estimated resources included herein are determined for 
specific deposits within the complex. Resource calculations 
are based upon published company information, Bureau and 
U.S. Geological Survey project reports and publications, 
and inferences from reasonable extensions of ore zones 
based on available geologic data. Maximum depth of 
chromitites at the Mountain View, Benbow, and Nye Basin 
is as has been arbitrarily fixed at the Stillwater River 
Valley, i.e., 1,525 m above sea level. This elevation 
represents the lowest surface exposure of chromitite layers. 
Resources total 42,441,000 mt averaging 22.2 pet Cr 2 3 
(table 4). 



TABLE 4.— Chromite resources of the Stillwater Complex 


Deposit 


Ore, mt 


Cr 2 3 grade, 
pet 


Mountain View Mine 

Benbow Mine 

Nye Basin Area 

Gish Mine 


15,104,000 

17,953,000 

8,530,000 

854,000 


22.6 
22.2 
22.2 
15.0 


Total 


42,441,000 


22.2 



Source: References 11 and 13 and Bureau estimates (1984). 



RED LODGE DISTRICT 

Chromite in the Red Lodge district occurs as lenses and 
pods scattered through sill-like masses of serpentinized 
peridotite that have intruded metasediments and meta- 
volcanic rocks. These metasediments and metavolcanics 
now exist as roof pendants in gneissoidal Precambrian 
granite, which underlies most of the Beartooth Range (15). 

Chromite was first discovered in the Red Lodge area in 
1916. The only recorded production, however, took place 
from 1941 to 1943 when 51,200 mt ore averaging 12.5 pet 
Cr 2 3 was mined and milled. This produced 10,600 mt con- 
centrate averaging 40 pet Cr 2 3 with a 1.4 Cr-Fe ratio (15). 
An additional 19,000 mt lump ore averaging 32 pet Cr 2 3 
was also produced during this time. 

Resource estimates for the Red Lodge district total 
18,000 mt averaging 30.0 pet Cr 2 3 (15). 



TABLE MOUNTAIN PROSPECT 

The Table Mountain prospect was investigated by the 
Bureau in 1965 during the wilderness study of the Spanish 
Peaks Primitive Area. The deposit area is composed of 
granitic gneiss, hornblende schist, amphibolite, and chloritic 
schist. The chromite occurs within the amphibolite and 
chloritic schist (1). The amphibolite lens is approximately 
100 m long and 10 m wide and is surrounded by an addi- 
tional 11 m of chromite-bearing chloritic schist. 

Resources are estimated at 352,000 mt averaging 10.6 
pet Cr 2 3 with Cr-Fe ratios between 1.5 and 1.7 (1). 



35 



CALIFORNIA 



Chromite resources in California total 6.9 million mt 
Cr 2 3 contained in 249.1 million mt of chromite-bearing 
material. Of this total, 1.5 million mt contained Cr 2 3 is low 
in Fe, with Cr-Fe ratios ranging between 2.5 and > 3, and 
2.5 million mt contained Cr 2 3 is high in Fe, with Cr-Fe 
ratios ranging between 1.6 and 2.2. The remaining 
resources consist of 2.75 millon mt Cr 2 3 in 103.9 million mt 
of lateritic soils, and 271,000 mt Cr 2 3 contained in 41.1 
million mt of asbestos resources. 

PODIFORM DEPOSITS 

Major podiform chromite resources in California are 
found in Siskiyou, Del Norte, El Dorado, San Luis Obispo, 
and Tehama Counties. 

Siskiyou County 
Seiad Creek District 

Principal deposits in the Seiad Creek district of Siskiyou 
County are the Emma Bell and Seiad Creek properties. 
These deposits have produced only 3,500 mt of lump ore and 
concentrates with an average Cr-Fe ratio of 3.0. However, 
exploration, which began in 1941 and is ongoing today, has 
delineated some of the largest domestic deposits discovered 
to date. From April to October 1941, the Bureau completed 
1,980 m of diamond drilling, 128 m of underground work- 
ings, and 956 m of trenching in an attempt to delineate the 
Seiad Creek deposit (34). In 1978, U.S. Chrome of Grants 
Pass, OR, initiated a diamond drilling program on its Seiad 
Creek property in an effort to expand the Bureau's work. 
By the end of 1978, seven drill holes totaling 508 m had been 
completed at the Seiad Creek Mine; three holes were drilled 
at the Emma Bell. During 1979, 14 more holes were drilled 
to delineate the upper portion of the Emma Bell. Drilling be- 
tween 1980 and 1982 totaled 493 m on three new target 
areas southeast of the Emma Bell; however, no significant 
chromite intercepts were encountered. 

In 1983, U.S. Chrome entered into a joint venture with 
Asamera Minerals. The partnership included the Seiad 
Creek, Emma Bell, Ladd, Fairview, and McGuffy Creek 
properties. Subsequent drilling at the Emma Bell consisted 
of two holes drilled by U.S. Chrome and two by Asamera. 

Resource estimates for the Emma Bell are based on a 
total strike length of 1,200 m, a width that ranges between 
20 and 50 m, and grades that average 3.4 pet Cr 2 3 . Higher 
grade chromite is concentrated within a 4- to 10-m width 
that averages 13.8 pet Cr 2 3 and contains an estimated 
466,000 mt Cr 2 3 in 3,384,000 mt ore. Should the lower 
grade material prove a viable resource in the future, an ad- 
ditional 149,000 mt Cr 2 3 contained in 14,558,000 mt ore is 
estimated to be available. 

The Seiad Creek deposit is located approximately 1.5 
km southeast of the southern end of the Emma Bell. The 
main ore body has a strike length of about 500 m with an 
average width of 45 m. The deposit hosts an estimated 
110,000 mt Cr 2 3 contained in 1,711,000 mt ore. 

Additional resources in the Seiad Creek district are 
small and probably do not exceed more than a few thousand 
metric tons of contained Cr 2 3 . 



Hamburg-McGuffy Creek Area 

The major deposits of the Hamburg-McGuffy Creek 
area are the Ladd and Fairview Mines and the McGuffy 
Creek deposits. Exploration in the Hamburg-McGuffy 
Creek area was initiated during the intense search for Cr 
during World War I. Considerable exploration and develop- 
ment took place during this period but ceased with the fall of 
Cr prices at war's end; little more than assessment work 
was carried out between 1918 and 1942. The U.S. Geological 
Survey, in accordance with the Strategic Minerals Act of 
1939, conducted an exploration program between May and 
June 1942 (34). The program consisted of 681 m of diamond 
drilling in the McGuffy Creek area. Ten holes were drilled 
on the Veta Chica Claim and four on the Cerro Colorado 
Claim. In addition, 150 trench channel samples were taken. 

At the Ladd property, U.S. Chrome Corp. drilled four 
holes totaling 460 m during the spring of 1979 (7). During 
this same period, surface sampling and mapping were con- 
ducted on the Fairview property. 

In fall 1983, Asamera Minerals began a diamond drilling 
program on the Veta Chica and Lady Grey Claims; by 
winter, over 1,000 m of drilling had been completed (19). 
During this period, Bureau personnel developed plane table 
maps of the Lady Grey, Veta Grande, Veta Chica, Grand 
Falls, and Grand Canyon Claims at McGuffy Creek; the 
Ladd Mine was also mapped. 

The largest chromite deposits in the McGuffy Creek 
area occur at the Veta Chica, Lady Grey, and Cerro Col- 
orado Claims. Minor deposits have been identified in the 
Grand Falls, Grand Canyon, and Veta Grande Claims. Total 
estimated resources for the McGuffy Creek deposits are 
37,000 mt Cr 2 3 contained in 417,000 mt ore. 

At the Ladd Mine, minimal diamond drilling and surface 
mapping has roughly delineated two subparallel zones of 
disseminated and schlieren chromite with a combined width 
of 21 m and a surface outcrop length of 550 m; drilling has 
intersected the zones at a depth of 100 m. The zones strike 
roughly N 10° to 20° E and dip 55° to 80° NW. Higher 
grade zones are estimated to contain 120,000 mt Cr 2 3 in 
1,605,000 mt ore. An additional 53,000 mt Cr 2 3 is con- 
tained in 3,497,000 mt dunite, which encloses the higher 
grade ore. 

Data on the Fairview Mine are restricted to a surface 
map (1 in = 50 ft) and 10 channel samples taken from sur- 
face outcrops (28). The deposit consists primarily of a zone 
of heavily disseminated to banded and massive chromite 
from < 1 m up to 3 m wide. The zone strikes roughly N 40° 
W and dips 65° to 85° SW. Surface exposures suggest a 
strike length of at least 150 m with no indication of the 
depth of downdip extension. Estimated resources are 
23,000 mt Cr 2 3 contained in 65,000 mt ore averaging 35.6 
pet Cr 2 3 with a 3.0 Cr-Fe ratio. 



Del Norte County 

Del Norte County is ranked second only to San Luis 
Obispo County for total production of chromite in Califor- 
nia. Through the end of the Government buying program in 
1958, more than 80 mines had produced a total of 86,600 mt 
of lump ore and concentrates (32, 36). Although more than 



36 



half the past production has come from high-grade massive 
podiform deposits, resources are estimated for only 12 high- 
grade deposits with a total of 60,000 mt averaging about 50 
pet Cr 2 3 with Cr-Fe ratios ranging between 2.8 and 3.7. 
The majority of these resources are contained in the High 
Plateau Mine, which has produced the highest quality 
domestic ore to date (55 pet Cr 2 3 with a 3.7 Cr-Fe ratio), 
and the French Hill Mine, which has produced more than 40 
pet of the total production in Del Norte County. Both 
deposits, as well as other massive occurrences in the region, 
contain pods, lenses, and tabular bodies of nearly pure 
chromite enclosed by highly serpentinized dunite along 
shear zones. 

The majority of the resources estimated for Del Norte 
County are contained in two deposits, the Bar Rick and the 
Broken Ladder. 

The Bar Rick deposit was discovered in 1952 by C. H. 
McClendon, who operated the property in conjunction with 
several others from 1953 to 1958 (18). Exploration of the 
deposit consists of 500 m of diamond drilling by Inspiration 
Development Co. in 1971, and subsequent surface sampling 
and mapping by the Bureau in 1979, 1980, and 1983. Addi- 
tional mapping and sampling were conducted by Del Norte 
Chrome Ltd., which purchased the property in 1981. 
Chromite resources are estimated by Del Norte Chrome at 
2,196,000 mt averaging 5.9 pet Cr 2 3 in the lower and upper 
benches, and 22,415,000 mt averaging 2.8 pet Cr 2 3 in the 
remainder of the deposit (5). Chromite in the upper and 
lower benches consists of lenses and streaks, and clots of 
more massive chromite, scattered randomly through highly 
sheared and serpentinized dunite. Dunite between the upper 
and lower benches is less altered and contains < 1 pet to 
> 10 pet disseminated chromite. 

The Broken Ladder deposit is located north of Gasquet 
Mountain. There is no recorded production or exploration 
history for the deposit; however, the Bureau mapped and 
sampled it in 1982 and 1983. Over a distance of more than 2 
km, chromite occurs as streaks and lenses in shear zones 
and as massive clots to sparsely disseminated grains in less 
altered dunite. Although additional work is required before 
more accurate resource estimates can be made, it is 
estimated that at least 300,000 mt Cr 2 3 contained in 6 
million mt of chromite-bearing material can be developed. 



El Dorado County 

The Pilliken Mine area contains the most significant 
chromite deposits in El Dorado County, with a total produc- 
tion through 1958 of 28,815 mt of lump ore and concen- 
trates (.4. 32). Deposits in the Pilliken area occur in 
peridotites of the Western Metamorphic Belt of the Sierra 
Nevada foothills. Nine distinct subareas within the Pilliken 
area contain potential chromite resources. Chromite occurs 
in a wide variety of forms, from sparsely disseminated 
grains to irregular masses of nearly pure chromite. 
Resource estimates were calculated from deposit descrip- 
tions and assay data provided by Wells (38) and Bureau sam- 
ple data collected in 1978 and 1979. The total resource 



potential for all nine areas consists of 344,000 mt Cr 2 3 con- 
tained in 3,284,000 mt ore and an additional 1,336,500 mt 
Cr 2 3 contained in 41,767,000 mt low-grade material. 
Resources are described in table 5. 

TABLE 5.— Estimated resources for the Pilliken area 



Location 


Ore, mt 


Cr 2 3 
grade, pet 


Contained 
Cr 2 3 , mt 


High-grade: 


1,770,000 

377,000 

636,000 

88,000 

44,000 

73,000 

278,000 

18,000 

41,767,000 


11.0 
9.0 
10.2 
10.2 
10.2 
9.6 
10.2 
7.2 

3.2 


194,700 


Subarea 2 


33,900 
64,900 




9,000 


Subarea 5 


4,500 
7,000 




28,400 




1,300 


Low-grade: 


1,336,500 






Total 


45,051,000 


3.7 


1,680,200 



Source: Reference 27 and Bureau estimates (1984). 

Although the Pilliken Mine area hosts the largest single 
group of podiform chromite deposits in California, the ma- 
jority of the lower grade ore contains unusually high quan- 
tities of Fe. Concentrates produced from ore containing < 5 
pet Cr 2 3 had Cr-Fe ratios ranging between 0.8 and 1.4, 
whereas concentrates produced from ore containing 5 to 15 
pet Cr 2 3 had Cr-Fe ratios averaging 1.7. These ratios are 
similar to those obtained from Stillwater ores. 

Resources have also been estimated for several smaller 
dunite masses that occur in El Dorado County. Six addi- 
tional properites, the Darrington, Steele, Joerger, Walker, 
Murphy, and Chaix, are estimated to contain 132,000 mt of 
chromite-bearing dunites averaging 12.0 pet Cr 2 3 (4, 38). 

San Luis Obispo County 

Chromite deposits in San Luis Obispo County comprise 
some of the largest past producers of disseminated chromite 
in California. Beginning as early as 1870, over 75 deposits 
have been developed that produced over 130,000 mt of low- 
Fe chromite concentrates and lump ore (32-33). A large ma- 
jority of this production came from the Castro, New Lon- 
don, La Primera, Trinidad, Pick and Shovel, Sealy, Sweet- 
water, and Norcross deposits. Chromite contained in these 
deposits generally ranged in grade between 5 and 20 pet 
Cr 2 3 . 

Several of the larger deposits were examined by the 
U.S. Geological Survey in the 1940's. In 1943, it was 
estimated that remaining resources were about 32,000 mt; 
however, during the 1950's, > 60,000 mt was mined. Cur- 
rently, total resources for San Luis Obispo County deposits 
have been estimated at 133,000 mt ore averaging 14.2 pet 
Cr 2 3 (27). Although the Bureau has yet to determine the 
potential of chromite resources in lower grade deposits con- 
taining 5 to 10 pet Cr 2 3 , the probability is high of discover- 
ing large tonnages of low-grade resources similiar to those 
described in Siskiyou, Del Norte, and El Dorado Counties. 
These deposits should be investigated in order to properly 
ascertain their potential. 



37 



Tehama County 

The North Elder Creek chromite deposits are located 
approximately 70 km west of Red Bluff in Tehama County. 
Nearly 32,000 mt of lump ore and concentrates have been 
produced from the Grau, Mill Gulch, and the Old Noble Elec- 
tric Steel Co. deposits (6, 32). All occur in a large shear zone 
more than 5 km in length and varying in width from a few to 
several hundred meters. Chromite occurs as pods, lenses, 
and streaks enclosed by serpentinized dunite and massive 
serpentine, or in varying degrees of dissemination within 
less altered dunite. 

Deposits of North Elder Creek were visited and sam- 
pled by the Bureau in 1979; a few disseminated resources 
are estimated to remain. Total resources are estimated at 
104,000 mt averaging 11.9 pet Cr 2 3 (22). Concentrates pro- 
duced during past operations averaged 45 pet Cr 2 3 with a 
2.8 Cr-Fe ratio. 

Since these resources are restricted to less than a few 
hundred meters of the total strike length, additional 
resources may be present north and south along strike. 

Other Areas 

Additional low-Fe resources are available in several 
smaller podiform deposits throughout California. These 
deposits are described in table 6. Deposits listed in table 6 
contain published resources only. Permission to disclose 



Bureau individual property estimates was not received prior 
to publication. 

LATERITE DEPOSITS 

Laterite resources in California are estimated at 
2,750,000 mt Cr 2 3 contained in 103,897,000 mt of lateritic 
soil. The bulk of these resources were delineated during the 
Bureau's field program, which commenced in 1976 and con- 
tinued through 1979. The majority of sampling was ac- 
complished with backhoes and hand augers. 

PLACER DEPOSITS 

The only known placer deposit of interest in California 
is the beach sand deposit that extends for about 7 km south 
of the breakwater at Whaler Island (36) just south of Cres- 
cent City. Within this area is a strip of concentrated black 
sands 3 km by 75 m to 110 m averaging 1.2 m thick. This 
zone is estimated to contain 700,000 mt averaging 7.0 pet 
Cr 2 3 . 

OTHER OCCURRENCES 

An additional 270,000 mt Cr 2 3 is contained in over 41 
million mt of asbestos resources in San Benito, Fresno, and 
Tulare Counties. 



TABLE 6.— Additional low-Iron resources from California podiform deposits 



Deposits by county 


Past production 


Cr-Fe 


Published resource 










Cr:0 3 , pet 


ratio 


Ore, mt 


Cr 2 3 , pet 


Reference 


Butte: 












Lambert 


44 


2.8 


W 


W 


W 


Parks Ranch 


38 


2.6 


W 


W 


W 


Del Norte: Sunrise 


47 


2.6 


W 


W 


W 


Fresno: 














46 
44 


3.0 
2.6 


W 
1,200 


W 
30.0 


17 


Jack Sprat 


23 




45 


2.6 


6,800 


8.0 


23 


Glenn: 














47 
47 


3.0 
3.0 


40,000 
151,000 


8.0 
12.9 


25 




25 


Nevada: Holsemann 


33 


2.5 


W 


W 


W 


Placer: Parker Ranch 


40 

45 


1.6 
2.8 


5,000 
5,000 


8.0 
23.0 


24 


Shasta: Little Castle Creek 


37 


Sierra: 












Milton 


30 


2.5 


W 


W 


W 


Oxford 


MA 


NA 


W 


W 


W 


Siskiyou: 














38 
54 


3.2 
3.3 


W 
100 


W 
54.4 


W 


Peg Leg 


35 




34 


2.5 


2,000 


33.8 


9 


Toulumne: 






35 
37 
NA 


3.2 
NA 
NA 


7,500 
7,000 

w 


15.0 

20.0 

W 


2 


Richards 


2 


North End 


W 


McCormick 


43-49 


2.8-3.5 


220 


47.0 


26 


Trinity: Black Bear 


NA 


NA 


W 


W 


W 






Total 


NAp 


NAp 


516,000 


16.8 


NAp 



NA Not available. NAp Not applicable. W Withheld; Included in total. 



38 



OREGON 



Chromite resources in Oregon total 4.8 million mt Cr 2 3 
contained in 306.7 million mt of chromite-bearing material. 
Of this total, 85,000 mt contained Cr 2 3 is low in Fe with Cr- 
Fe ratios ranging between 2.2 and 2.8; 2,409,100 mt con- 
tained Cr 2 3 is high in Fe with Cr-Fe ratios ranging be- 
tween 1.4 and 2.0. Remaining resources consist of 2,323,000 
mt Cr 2 3 in 92,922,000 mt of lateritic soils. 

PODIFORM DEPOSITS 

Major podiform chromite resources are found in the 
Josephine Peridotite located in portions of Josephine, 
Curry, Douglas, Jackson, and Coos Counties, and in the 
John Day area in Grant County. 

Josephine Peridotite 

Production from podiform deposits in the Josephine 
Peridotite totals 49,000 mt of lump ore averaging 48 pet 
Cr 2 3 with a 2.8 Cr-Fe ratio, and approximately 2,000 mt of 
concentrates averaging 46 pet Cr 2 3 with a 2.5 Cr-Fe ratio. 
Production has come from 58 properties in Josephine Coun- 
ty, 19 in Curry County, 8 in Douglas County, 5 in Jackson 
County, and 2 in Coos County (20). Most of the deposits 
were high-grade lenses and pods that yielded less than a few 
hundred metric tons. The Oregon Chrome Mine, however, 
accounted for nearly 65 pet of the area's total production. 

Only four deposits, the Oregon Chrome Mine, Chrome 
King, Shady Cove, and Dirty Face, have data available for 
determining high-grade resource potential. These contain 
an estimated 25,000 mt of nearly pure, massive chromite in 
the form of pods, lenses, and tabular bodies enclosed by 
highly serpentinized dunite. This resource averages 45 pet 
Cr 2 3 with a Cr-Fe ratio of 2.7. 

Areas of significant resource potential include the 
Chrome Ridge area in Josephine County and the Sourdough 
area in Curry County. 

The Chrome Ridge area was investigated by the Bureau 
in 1983 and 1984; the deposits were mapped and 150 
samples were collected. Three principal deposits with 
significant resources were identified: the Violet, Buster, 
and Shady Cove. 

The Violet Mine consists of upper and lower workings 
situated along two shear zones in highly serpentinized and 
chloritized dunite. The upper workings are in a north- 
northwest-trending zone 6 m wide by almost 100 m long. 
The lower zone workings, some 100 m to the southwest, 
average 15 m wide over a 35-m strike length. 

The Buster Mine lies in serpentinized dunite and is 
faulted against metamorphosed harzburgite along the 
western edge of the deposit. Chromite occurs as dissemina- 
tions within the dunite and as layers in shear zones. Sam- 
pling from lower and upper benches defined a zone 25 m 
wide and 45 m long. 



The Shady Cove Mine contains schlieren-type banded 
chromite in serpentinized shear zones associated with 
northeast-trending faults. Small massive chromite pods are 
associated with the serpentinite. Analyses of the massive 
chromite average 41.8 pet Cr 2 3 and 55.0 pet Cr 2 3 plus 
A1 2 3 , with a 2.9 Cr-Fe ratio. 

Resource estimates total 200,000 mt at the Violet 
averaging 4.7 pet Cr 2 3 , 321,000 mt at the Buster averag- 
ing 8.3 pet Cr 2 3 , and 10,000 mt at the Shady Cove averag- 
ing 19.4 pet Cr 2 3 . 

Resources have been estimated for the Sourdough area 
by Wells (39) at 100,000 mt averaging 15 pet Cr 2 3 , and for 
the Young's Dailey Dozen by Ramp (20) at 20,000 mt averag- 
ing 15 pet Cr 2 3 . 

Detailed mapping and sampling should increase these 
estimates considerably. 



John Day Area 

Chromite deposits in the John Day District, Grant Coun- 
ty, contain mostly high-alumina chromite with as much as 27 
pet A1 2 3 (29). The three most significant deposits were ex- 
plored by trenching and shallow diamond drilling by the 
Bureau in the 1940's. The deposits contain lenses of heavily 
disseminated to massive chromite enclosed by serpentized 
dunite. Bureau estimates are 113,000 mt averaging 23 pet 
Cr 2 3 with a 1.8 Cr-Fe ratio for the Chambers Mine, 68,000 
mt averaging 22 pet Cr 2 3 for the Iron King Mine, and 
7,500 mt averaging 20 pet for the Dry Camp Mine (12). 



LATERITE DEPOSITS 

Laterite resources in Oregon are estimated at 2,323,000 
mt Cr 2 3 contained within 92,922,000 mt of lateritic soil. 
The bulk of these resources were delineated between 1976 
and 1979 during the Bureau's field program. 



PLACER DEPOSITS 

Black sand deposits occur on raised marine terraces 
along the southern coast in Coos and Curry Counties. Con- 
centrations of black sands are found as lenses and layers 
that range from a few centimeters to more than 12 m thick 
(8). Detailed investigations, including drilling, were initiated 
in the 1940's and have continued intermittently through 
1980. Drilling by the Bureau during the 1970's totaled more 
than 100 holes. 

Production of chromite from the higher grade deposits 
occurred during World War II and the Korean War, during 



39 



which time 1,844,800 mt of sands averaging 3.8 pet Cr 2 3 
were mined and concentrated. Not all of the material mined 
was concentrated to a final product. Total shipped concen- 
trates were 48,600 mt averaging 39.3 pet Cr 2 3 with a 1.5 
Cr-Fe ratio. 

Resources estimates for individual deposits were de- 
rived from published U.S. Geological Survey and Bureau 
reports, and from reasonable extensions based on the 
Bureau's drilling in the 1970's. This resource is estimated to 
contain 384,500 mt Cr 2 3 in 8,068,700 mt of black sands. 
The source of these estimates is described in table 7. 

Additional resources are probably vast; however, addi- 
tional drilling would be required to determine the full poten- 
tial. Drilling to date in the vicinity of the Seven Devils and 
Whiskey Run terraces suggests the presence of at least 2 
million mt Cr 2 3 contained in 200 million mt of black sands. 



TABLE 7.— Southwest Oregon beach sand deposits 



Deposit 


Ore, 


Cr 2 Oj grade, 


Contained 




mt 


pet 


Cr 2 3 , mt 


South slough 


1,995,800 


3.25 


64,900 


Section 33 


1,274,000 


3.93 


50,200 


Section 4 


719,600 


5.02 


36,100 


Seven Devils 


1,236,200 


5.85 


72,300 


Seven Devils area . . . 


144,200 


7.80 


11,200 


Whiskey Run area . . . 


99,000 


6.20 


6,100 


Shepard Mine 


257,500 


7.04 


18,100 


Shepard Extension . . 


1,436,000 


3.35 


48,100 


Pioneer-Eagle 


470,000 


8.80 


41,400 


Butler Mine 


62,200 


8.70 


5,400 


The Lagoons 


124,200 


10.60 


13,200 


Madden 


100,000 


10.00 


10,000 


Others 


150,000 


5.00 


7,500 


Total 


8,068,700 


4.77 


384,500 







Source: Reference 8 and Bureau estimates (1978). 



WASHINGTON 



Estimated resources in Washington State total 30,700 
mt of low-iron Cr 2 3 . Additional resources present in iron 
ore deposits total 221,700 mt Cr 2 3 . 



PODIFORM DEPOSITS 

Low-Fe chromite in Washington occurs as lenses, pods, 
and disseminated crystals in the Twin Sisters area of What- 
com and Skagit Counties. 

The Twin Sisters area contains a mass of dunite 11 km 
long and 5 km wide that is a major source of olivine for foun- 
dry sand. Chromite deposits on the south summit of the 
Twin Sisters Range consist of small lenses and pods 
estimated to contain 30,700 mt Cr 2 3 in 470,000 mt of 
chromite-bearing material (16). The potential for large ton- 
nages of lower grade resources in a dunite of this size is ex- 
ceedingly high, and investigation of the area is warranted. 



OTHER OCCURRENCES 

Chromium contained in iron ore deposits in the Blewett 
Pass and Cle Elum areas may provide a future source of 
domestic chromite. The Cle Elum deposit consists of ir- 
regular lenses of iron ore in a serpentized peridotite. Exten- 
sive diamond drilling by the Bureau delineated a total 
resource of 7,520,000 mt averaging 2.6 pet Cr 2 3 , 42 pet Fe, 
and 0.93 pet Ni. The principal iron minerals are magnetite, 
hematite, and limonite that occur intermixed with serpen- 
tine and olivine. 

The Blewett Pass deposit is similar to the Cle Elum, but 
smaller and lower in grade; however, additional resource is 
contained in the conglomerate that overlies the deposit. The 
total resource consists of 41,900 mt of iron ore averaging 
2.48 pet Cr 2 O s> 32.5 pet Fe, and 0.88 pet Ni, and 3,029,400 
mt of conglomerate averaging 0.88 pet Cr 2 3 , 11.5 pet Fe, 
and 0.4 pet Ni (21). 



WYOMING 



The only significant occurrence of chromite in Wyoming 
is the Casper Mountain deposit located in Natrona County. 
The deposit, a high-Fe, chromite-bearing, actinolite-talc 
schist, was investigated by the U.S. Geological Survey as 
early as 1934 and drilled by the Bureau in 1939. The Bureau 
program included 1,105 m of drilling and 24 surface trench- 
es (10). This work delineated two schist bodies containing a 



total of 3,774,900 mt averaging 2.5 pet Cr 2 3 , including 
higher grade resources of 521,500 mt averaging 8.7 pet 
Cr 2 3 (10). 

These resources were calculated to a depth of 30 m, and 
drilling indicates that additional resources may persist to a 
depth of 150 m. 



40 



APPALACHIAN STATES 



Estimates of chromite resources in the Appalachian 
States are restricted to placer deposits in the State Line 
district of Pennsylvania and Maryland and smaller areas in 
North Carolina and Georgia. Although the State Line 
district produced at least 254,000 mt of high-Fe (Cr-Fe 
ratios averaging 1.6) chromite from podiform deposits prior 
to 1900, little work has been done to determine if additional 
resources remain. However, resource estimates were made 



by the Bureau of Mines for 18 placer deposits derived from 
weathering of the podiform deposits. Past production from 
these deposits was estimated to total 19,000 mt concen- 
trates (16). 

Resource estimates for 9 deposits in Maryland, 5 in 
Pennsylvania, 3 in North Carolina, and 1 in Georgia total 
1,247,000 mt averaging 1.4 pet Cr 2 3 for the 18 deposits. 



SUMMARY 



The total available chromite in the conterminous United 
States is estimated at 21,554,100 mt Cr 2 3 (fig. 2). 

The known low-Fe Cr resources in the conterminous 
United States are in the California, Oregon, and Washing- 
ton podiform deposits, and the majority of the total 1.6 
million mt Cr 2 3 is contained in the lower grade (5 to 20 pet 
Cr 2 3 ) disseminated deposits (95 pet) associated with the 
more massive smaller pods and lenses exploited in the past 
(fig. 3). Additional low-Fe resources similar to those iden- 
tified in Siskiyou and Del Norte Counties, CA, and the 
Chrome Ridge area of Josephine County, OR, may be de- 
veloped by detailed mapping and sampling of deposits in 
San Luis Obispo County, CA, Curry County, OR, and the 
Twin Sisters area of Whatcom and Skagit Counties, WA. 



Washington 

1.1 pet 

252,400 

mt 



Wyoming 
0.4 pet 
92,500 mt Appalachian States 

0.1 pet 

17,000mt 




TOTAL: 22 million mt 
of contained Cr 2 3 



The primary source for high-Fe Cr is the Stillwater 
Complex, MT. Approximately 75 pet of the total 12.4 million 
mt Cr 2 3 estimated is contained in Stillwater stratiform 
deposits (fig. 3). Other major sources of high-Fe Cr are large 
low-grade (3 to 5 pet Cr 2 3 ) podiform deposits in the 
Western States such as the Pilliken deposit in El Dorado 
County, CA, or the black sand deposits of Coos and Curry 
Counties, OR. Additional high-Fe resources may be de- 
veloped by continued exploration of the black sand deposits 
in Oregon and northwest area podiform deposits. 

Domestic sources of high-alumina refractory chromite 
are located principally in the John Day area of Grant Coun- 
ty, OR. For this study, these deposits are combined with the 
high-Fe resource. Other sources of refractory-quality 
chromite have been found associated with podiform deposits 
elsewhere in Oregon and California; however, most deposits 
are small. 




TOTAL: 22 million mt 
of contoined Cr-O* 



FIGURE 2.— Total estimated resources by State. 



FIGURE 3.— Total estimated resources by type. 



41 



REFERENCES 



1. Becraft, G. E., J. W. Calkins, E. C. Pattee, R. D. Weldin, and 
J. M. Roche. Mineral Resources of the Spanish Peaks Primitive 
Area, Montana. U.S. Geol. Surv. Bull. 1230-B, 1966, pp. B11-B15. 

2. Cater, F. W., Jr. Chromite Deposits in Tuolumne and Mariposa 
Counties, California. Ch. 1 in Geologic Investigations of Chromite 
in California. CA Div. Mines Bull. 134, pt. 3, 1948, pp. 1-32. 

3. . Chromite Deposits in Calaveras and Amador Counties, 

California. Ch. 2 in Geologic Investigations of Chromite in Califor- 
nia. CA Div. Mines Bull. 134, pt. 3, 1948, pp. 33-60. 

4. Cater, F. W., Jr., G. A. Rynearson, and D. H. Dow. Chromite 
Deposits of El Dorado County, California. Ch. 4 in Geologic In- 
vestigations of Chromite in California. CA Div. Mines Bull. 134, pt. 
3, 1951, pp. 105-167. 

5. Del Norte Chrome Corp. Ltd. (Vancouver, BC, Canada). An- 
nual Report, Year Ended 1982. 6 pp. 

6. Dow, D. H., and T. P. Thayer. Chromite Deposits of the North- 
ern Coast Ranges. Ch. 1 in Geologic Investigations of Chromite in 
California. CA Div. Mines Bull. 134, pt. 2, 1946, pp. 1-38. 

7. Frizzell, L. (U.S. Chrome Corp.). Private communication, 
1980; available upon request from N. Wetzel, BuMines, Spokane, 
WA. 

8. Griggs, A. B. Chromite-Bearing Sands of the Southern Part of 
the Coast of Oregon. U.S. Geol. Surv. Bull. 945-E, 1945, pp. 
133-150. 

9. Hawkes, E. H., Jr., F. G. Wells, and D. P. Wheller, Jr. 
Chromite and Quicksilver Deposits of the Del Puerto Area, 
Stanislaus County, California. U.S. Geol. Surv. Bull. 936-D, 1942, 
pp. 93-94, 98-101. 

10. Horton, F. W., and P. T. Allsman. Investigation of Casper 
Mountain Chromite Deposits, Natrona County, Wyoming. BuMines 
RI 4512, 1949, 26 pp. 

11. Howland, A. L., E. M. Garrels, and W. R. Jones. Chromite 
Deposits of Boulder River Area, Sweetgrass County, Montana. 
U.S. Geol. Surv. Bull. 948-C, 1949, pp. 63-82. 

12. Hundhausen, R. J., L. H. Banning, H. M. Harris, and H. J. 
Kelly. Exploration and Utilization Studies, John Day Chromite, 
Oregon. BuMines RI 5238, 1956, 67 pp. 

13. Jackson, E. D. Primary Textures and Mineral Associations in 
the Ultramafic Zone of the Stillwater Complex, Montana. U.S. 
Geol. Surv. Prof. Paper 358, 1961, 106 pp. 

14 The Chromite Deposits of the Stillwater Complex, Mon- 
tana. Sec. in Ore Deposits in the United States, 1933-1967 (Graton 
Sales). AIME, v. 2, 1968, pp. 1495-1510. 

15. James, H. L. Chromite Deposits Near Red Lodge, Carbon 
County, Montana. U.S. Geol. Surv. Bull. 945-F, 1946, p. 151. 

16. Kingston, G. A., R. A. Miller, and F. V. Carrillo. Availability 
of U.S. Chromium Resources. BuMines IC 8465, 1970, 23 pp. 

17. Matthews, R. A. Geology of the Butler Estate Chromite Mine, 
Southwestern Fresno County, California. CA Div. Mines and Geol., 
Spec. Rep. 71, 1961, 19 pp. 

18. McClendon, B. Private communication, 1981; available upon 
request from N. Wetzel, BuMines, Spokane, WA. 

19. Neimeyer, W. (Asamera Minerals Inc.). Private communica- 
tion, 1984; available upon request from N. Wetzel, BuMines, 
Spokane, WA. 

20. Ramp, L. Chromite in Southwestern Oregon. OR Dep. Geol. 
and Min. Ind., Bull. 52, 1961, 169 pp. 

21. Ravitz, S. F. Electric Smelting of Low-Grade Nickel Ores. 
BuMines RI 4122, 1947, 39 pp. 



22. Rynearson, G. A. Chromite Deposits of the North Elder 
Creek Area, Tehama County, California. U.S. Geol. Surv. Bull. 
945-G, 1946, pp. 208-209. 

23 Chromite Deposits of Tulare and Eastern Fresno Coun- 
ties, California. Ch. 3 in Geologic Investigations of Chromite in 
California. CA Div. Mines Bull. 134, pt. 3, 1948, pp. 61-104. 

24. Chromite Deposits in the Northern Sierra Nevada, 

California. Ch. 5 in Geologic Investigations of Chromite in Califor- 
nia. CA Div. Mines Bull. 134, pt. 3, 1953, pp. 168-323. 

25. Rynearson, G. A., and F. G. Wells. Geology of the Grey Eagle 
and Some Nearby Chromite Deposits in Glenn County, California. 
U.S. Geol. Surv. Bull. 945-A, 1944, p. 14. 

26. Shuttuck, J. C. McCormick Chromite Mine, Tuolumne Coun- 
ty, California. BuMines RI 4578, 1949, 15 pp. 

27. Smith, C. T., and A. B. Griggs. Chromite Deposits Near San 
Luis Obispo, San Luis Obispo County, Calif. U.S. Geol. Surv. Bull. 
945-B, 1941, 44 pp. 

28. Strickler, M. (Lithologic Resources Inc.). Private communica- 
tion, 1983; available upon request from N. Wetzel, BuMines, 
Spokane, WA. 

29. Thayer, T. P. Chromite Deposits of Grant County, Oreg. U.S. 
Geol. Surv. Bull. 922-D, 1940, pp. 75-113. 

30. Todd, S. G., D. W. Keith, L. W. LeRoy, D. J. Schissel, E. L. 
Mann, and T. N. Irvine. The J-M Platinum-Palladium Reef of the 
Stillwater Complex, Montana: I. Stratigraphy and Petrology. 
Econ. Geol. and Bull. Soc. Econ. Geol., v. 77, No. 6, Sept-Oct. 1982, 
pp. 1454-1480. 

31. Turner, A. Anaconda Copper Company Stillwater Pro- 
ject-Chrome. Company rep., Feb. 1980, 32 pp.; available upon re- 
quest from N. Wetzel, BuMines, Spokane, WA. 

32. U.S. Bureau of Mines. Minerals Yeakbooks 1940-58. Chapters 
on California, Oregon, Washington, Pennsylvania, Maryland, 
Wyoming, and Montana. 

33. Walker, G. W., and A. Griggs. Chromite Deposits of the 
Southern Coast Ranges of California. Ch. 2 in Geologic Investiga- 
tions of Chromite in California. CA Div. Mines Bull. 134, pt. 2, 
1953, pp. 39-88. 

34. Wells, F. G. Chromite Deposits Near Seiad and McGuffy 
Creeks, Siskiyou County, California. U.S. Geol. Surv. Bull. 948-B, 
1949, 62 pp. 

35. Wells, F. G., and F. W. Cater, Jr. Chromite Deposits of 
Siskiyou County. Ch. 2 in Geologic Investigations of Chromite in 
California. CA Div. Mines Bull. 134, pt. 1, 1950, pp. 77-127. 

36. Wells, F. G., F. W. Cater, Jr., and G. A. Rynearson. Chromite 
Deposits of Del Norte County. Ch. 1 in Geologic Investigations of 
Chromite in California. CA Div. Mines Bull. 134, pt. 1. 1946, pp. 
1-76. 

37. Wells, F. G., and H. E. Hawkes. Chromite Deposits of Shasta, 
Tehama, Trinity, and Humboldt Counties. Ch. 3 in Geologic In- 
vestigations of Chromite in California. CA Div. Mines Bull. 134, pt. 
1, 1965, pp. 128-191. 

38. Wells, F. G., L. R. Page, and H. L. James. Chromite Deposits 
of the Pilliken Area, El Dorado County, California. U.S. Geol. Surv. 
Bull. 922-0, 1940, pp. 417-460. 

39 . Chromite Deposits in the Sourdough Area, Curry Coun- 
ty, and the Briggs Creek Area, Josephine County, Oregon. U.S. 
Geol. Surv. Bull. 922-P, 1940, pp. 461-492. 



43 



EXTRACTIVE METALLURGY SESSION 

Chairman: Charles B. Daellenbach 

Research Supervisor 

U.S. Bureau of Mines 

Albany Research Center 

P.O. Box 70 

Albany, OR 97321 



BuMines IC 9087: Chromium-Chromite: Bureau of Mines Assessment and Research 



45 



COPRODUCT CHROMITE FROM NICKEL— BEARING LATERITES 

By Donald E. Kirby 1 and Donald R. George 2 

ABSTRACT 



The Bureau of Mines developed a process to recover 
chromite from nickel-bearing laterites in the Western 
United States. The laterite deposits are extensive but low 
grade, and their value as a resource is dependent on 
recovery of contained Ni and Co in addition to the chromite. 
In the present investigation, emphasis was placed on 
recovering chromite from the residues remaining after Ni 



and Co extraction. Both the unprocessed laterites and the 
laterite residues responded to standard ore dressing 
methods, but Cr recovery was generally below 50 pet and 
concentrate grades were 29 to 40 pet Cr 2 3 . The low yields 
and grades resulted from fine particle size of the chromite 
and the gangue. 



PACIFIC COAST LATERITES 



Laterites of southwestern Oregon and northern Califor- 
nia are the largest secondary deposit of chromium in the 
United States (1). These laterites are soils -the product of 
chemical weathering of peridotite rocks exposed to tropical 
or subtropical climates. In the laterization process the Ca, 
Mg, and Si0 2 constituents of the rock are dissolved and 
leached away. The Co, Cr, Fe, and Ni resist leaching and 
become enriched in the lateritic residual soils. 

Laterite mineralogy is variable; it includes primary 
minerals of the original peridotite and secondary minerals 
resulting from its weathering. The predominant mineral is 
goethite, a hydrated iron oxide, FeO(OH), which contains 
most of the nickel. A wadlike manganese oxide mineral (as- 
bolite) contains most of the cobalt. Other minerals are com- 
monly found in smaller amounts: massive and fibrous 
serpentine, chlorite, quartz, talc, hematite, tremolite, and 
enstatite. Chromite and magnetite present in the original 
rock resist weathering; they are found in the laterites 
chemically unchanged, but concentrated by removal of the 
other constituents. 

Mineral particles in the chromite-bearing laterites are 
very fine grained. The average particle diameter is about 8 
jtm. The chromite in laterite has an average particle 
diameter between 100 and 200 /*m, and it is usually present 
as a high-Fe spinel containing a maximum of 50 pet Cr 2 3 
and having a Cr-Fe ratio of 1.9. 

The typical laterites processed in this study contain 2.8 
to 4.1 pet chromite. It is doubtful that such a low-grade Cr 
resource could be used were it not for its size and the 
presence of other valuable constituents (Ni and Co). 
Laterites containing significant Ni and Co values and ap- 
preciable Cr cover a sizable area of northern California and 
southwestern Oregon, as shown in figure 1. It is estimated 
that this laterite resource exceeds 217 million st (2), and 
there are additional Ni-bearing laterites located farther 
south in California; e.g., in Mendocino County. The laterites 
examined contain 0.7 to 1.1 pet Ni and 0.06 to 0.10 pet Co in 
addition to 1.9 to 2.8 pet Cr 2 3 . 



1 Metallurgist. 

2 Engineering technician. 

Albany Research Center, Bureau of Mines. P.O. Box 70, Albany, OR 
97321. 



The Bureau of Mines developed a hydrometallurgical 
process to recover Ni and Co from laterites. This four-step 
process includes (1) low-temperature selective reduction, (2) 
extraction by ammonia-ammonium sulfate solution under 
oxidation conditions, (3) separation and concentration of the 
values by liquid ion exchange, and (4) recovery of Ni and Co 
as pure metals by electrowinning (3). 

The residue from this process is finer than the original 
laterite. Its color is changed from reddish orange to black as 
its Fe content is partly reduced. Although nearly all the Ni 
and Co content of the laterite is removed and recovered, the 
chromite is unchanged during processing except for a slight 
size reduction. 



Abbreviations Used in This Paper 



/tm 


micrometer 


pet 


weight percent 


st 


short ton 


st/d 


short ton per day 



N 



PACIFIC 
OCEAN 



Port Orford' 



Gold Beach ) 



KEY 

A Laterite deposit 
• Town or city 



Brookings 



Pacific Coast 
Laterites 



Grants Pass 

A Red Flat 

Eight Dollar Mtn 

Woodcock Mtn A 

Rough and 

Ready Cr 

PinWlof 

Gasque't Mtn 



Crescent Cityv 




, Rattlesnake Mtn 



FIGURE 1.— Pacific coast laterites. 



46 



CHROMITE BENEFICIATION 



FLOWSHEET DEVELOPMENT AND RESULTS 

The low grade and fine size of chromite would make the 
laterite materials a very questionable Cr resource were it 
not for the accompanying Ni and Co values. For laterite to 
be considered a Cr resource, it must be appraised primarily 
for the recovery of the Ni and Co values and secondarily for 
the coproduction of the Cr values. 

In this study, the primary efforts to recover chromite 
from laterite were directed toward processing the residues 
following Ni and Co extraction. The low Cr values in the 
residue suggested a low-cost approach using physical ore 
dressing methods, although both the residues and un- 
processed laterites were finer than appropriate for many of 
these processing methods. Methods investigated included 
gravity concentration, flotation, low- and high-intensity 
magnetic separation, electrostatic separation, sizing, and 
combinations of these. 

Examination and characterization of a variety of 
laterites and laterite residues indicated that the coarsest 
fractions were predominantly serpentine, low in chromite 
content, and the finest fractions were either goethite or 
partly reduced goethite and also low in chromite content (b). 
As a result of these findings the general processing 
flowsheet shown in figure 2 was developed, taking advan- 
tage of differences in mineral size, specific gravity, and 
magnetic properties. Using this flowsheet, sizing rejected 
more than three-quarters of the total feed weight, but less 
than half of the chromite. Screening removed the coarse 
waste, and hydrocycloning removed the fine waste. The 
chromite that is lost to the finest fraction was unrecoverable 
by any known methods. Among methods used to attempt 
scavenging chromite from the slimes were flotation, elutria- 
tion, and sizing with smaller hydrocyclones to produce finer 
cuts. 

The intermediate product, finer than minus 65 mesh 
and coarser than 10 ^m, was then treated by two stages of 
low-intensity magnetic separation to reject the bulk of the 
naturally occurring magnetite and some of the partly re- 
duced goethite, although the latter was too fine to respond 
well to magnetic separation. 

The nonmagnetic fraction, enriched in chromite, was 
classified further at about 200-mesh equivalent size prior to 
feeding it to two parallel gravity circuits, one processing the 
coarser fraction and the other the finer fraction. A shaking 
table, shown in figure 3, was used in the two gravity cir- 
cuits. Both circuits used a rougher step followed by a second 
tabling step in which the rougher middlings were retreated. 
About 80 pet of the chromite contained in the minus 65- plus 
200-mesh sands reported to the concentrate. However, only 
about 35 pet of the chromite was recovered from the minus 
200-mesh fraction in dual tabling. The table middlings from 
this operation were essentially a fine, liberated mixture of 
chromite and enstatite, MgSi0 3 , a pyroxene mineral. A two- 
stage treatment of these middlings on a Bartles-Mozley 3 
separator, a gravity concentrator designed to scavenge and 
recover heavy minerals fines from slimes, increased 
recovery in the chromite slime circuit by 8 to 18 pet. Results 
shown in table 1 are typical of the chromite grade and Cr 
recovery values, both with and without scavening, that 



might be expected from beneficiating laterite residues. In 
this case, processing results are shown for Red Flat and 
Rough and Ready Creek materials. Both deposits are 
located in southwest Oregon. 

Loterite or Laterite Leach Residue 



SIZING 
(SCREEN) 



-Oversize- 



SIZING 

(hydrocyclone: 



Undersize- 



MAGNETIC 
SEPARATION 



Magnetic 



GRAVITY 
CONCENTRATION 



product 
Table 



tailings 



Chromite Concentrate 



Rejects 



FIGURE 2.— Chromite from laterite or laterite leach residue. 



3 Reference to specific products does not imply endorsement by the Bureau 
of Mines. 




FIGURE 3.— Table concentration of chromite from laterite. 



47 



Most of the developmental work on the benefication 
system for recovering chromite from laterite was done us- 
ing leach residue from the V4-st/d, Ni-Co extraction 
miniplant operated at the Bureau's Albany Research 
Center. As an alternative to processing residues after 
hydrometallurgical treatment, untreated laterite was 
studied as a feed to the chromite benefication circuit. Raw 
laterite from the Rough and Ready Creek deposit was 
chosen for these studies as it represented a fairly typical 
laterite material. Results of these benefication tests are 
summarized in table 1. Recovery from the untreated laterite 
was comparable to that from residues, but the grade was 
somewhat lower. This is the result of improved mineral 
liberation in the extraction process residue. As can be seen, 
the Cr content of the benefication concentrates from either 
untreated laterites or residues is much lower than that of 
either commercial lump ore or concentrates. Values for the 
latter typically range between 40 and 50 pet Cr 2 3 . 
Chromium recoveries are low when compared to those from 
most beneficiation processes, in which overall recovery of 
values normally ranges from 70 to 95 pet. Grade and 



TABLE 1.— Miniplant beneficiation of laterite and laterite leach 
residue 





Cr 2 Oj 


Concentrate 


Beneficiation feed 


recovery, 


Cr 2 3 


Cr-Fe 




pet 


grade, pet 


ratio 


Red Flats residue: 








Without scavenging . . . 


35 


34 


1.6 


With scavenging 


53 


33 


1.6 


Rough and Ready Creek 








residue: 








Without scavenging' . 


36 


29 


1.9 


Without scavenging 2 . 


26 


37 


1.6 


With scavenging .... 


44 


29 


1.6 


Rough and Ready Creek 








untreated laterite: 








With scavenging 


40 


25 


1.4 



'Beneficiation for Cr recovery. 
2 Beneflciatlon for Cr grade. 



recovery are usually a trade-off -increase one and the other 
decreases. In chromite recovery from laterite, both grade 
and recovery are low -the result of attempting to recover a 
very fine concentrate from an extremely fine, slimy gangue 
by methods better suited to treating coarser materials. 

PILOT PLANT OPERATIONS 

The Bureau's successful development of processing 
technology for the Oregon and California laterite materials 
and the operation of Ni-Co extraction and chromite 
beneficiation miniplants encouraged further work on a 
larger, continuous scale. A contract was let by the Bureau of 
Mines to the Mineral Sciences Division of UOP Inc. to 
undertake the research effort. A 5-st/d hydrometallurgical 
pilot plant for extracting and recovering Ni and Co from 
laterite materials was assembled and operated at Tucson, 
AZ (5). During the operation of the Ni-Co pilot plant, a 
beneficiation circuit was operated for recovering chromite 
from the residues. 

The chromite beneficiation circuit at Tucson was in- 
complete. Coarse screening (65 mesh), hydrocycloning, 
rougher-sand tabling, and magnetic separation operations 
were performed at Tucson. The nonmagnetic products from 
low-intensity magnetic separators and the screening and 
tabling products were shipped to the Albany Research 
Center, where beneficiation was completed. The flowsheet 
for the entire benefication circuit is shown in figure 4. Prod- 
uct analyses and distributions are shown in table 2. These 
analyses and recovery figures reflect the operating per- 
formance of both the pilot plant in Tucson and the Bureau's 
miniplant. It was determined that an overall Cr recovery of 
46 pet as a concentrate containing 40 pet Cr 2 3 with a 1.8 
Cr-Fe ratio is achievable. The concentrate was used suc- 
cessfully to prepare a ferrochromium alloy and water- 
soluble Cr salts. These results are described elsewhere in 
this publication. 



TABLE 2.— Product stream analyses and distributions from pilot plant beneficiation of Rough and Ready Creek laterite leach residue 



Stream 


Stream name 


Analysis, pet 


Distribution, 


pet 


No. 


Cr 2 3 


Fe 


SI0 2 


MgO 


Al 2 0, 


Cr 


Fe 


Weight 


1 


Rough and Ready Creek 




















residue 


3.6 


32.8 


19.4 


11.8 


7.0 


100.0 


100.0 


100.0 


2 




1.2 
3.8 


12.3 
34.2 


36.7 
18.2 


24.3 
10.5 


4.1 
7.2 


3.2 
96.8 


2.9 
97.1 


7.0 


3 




93.0 


4 


Hydrocyclone overflow 


2.0 


38.4 


15.8 


8.1 


6.8 


41.0 


86.5 


73.8 


5 


Hydrocyclone underflow 


10.5 


18.2 


27.4 


19.8 


8.6 


55.8 


10.6 


19.2 


6 


Magnetic product 


5.5 


54.1 


5.8 


3.4 


6.0 


4.8 


4.9 


3.0 


7 


Nonmagnetic product 


11.4 


11.6 


31.3 


22.9 


9.1 


51.0 


5.7 


16.2 


8 


Classifier sands 

Rougher sand table: 


12.7 


9.4 


32.1 


24.3 


8.7 


27.9 


2.3 


8.0 


9 


Concentrate 


41.0 


15.1 


4.2 


14.4 


21.3 


18.0 


.7 


1.6 


10 


Tailings 

Middlings 


1,9 


7.2 


42.8 


28.2 


2.7 


3.0 


1.3 


5.8 


11 


17.4 


9.5 


31.1 


26.0 


13.8 


9.1 


.6 


1.9 




Scavenger sand table: 


















12 


Middlings 


6.1 


6.9 


43.8 


31.8 


5.1 


2.2 


.3 


1.3 


13 


Concentrate 


41.8 


15.1 


3.6 


13.6 


21.9 


6.9 


.3 


.6 


14 




10.2 


13.9 


30.6 


21.5 


9.5 


23.1 


3.4 


8.2 




Rougher slime table: 




15 


Concentrate 


41.4 


16.1 


1.7 


12.4 


22.3 


4.5 


.2 


.4 


16 




2.3 
10.5 


12.4 
13.9 


41.5 
31.3 


26.9 
21.6 


4.6 
9.2 


.4 
18.2 


.2 
3.0 


.6 


17 


Middlings 


7.2 




Scavenger slime: 


















18 




.9 
18.7 


13.4 
11.7 


41.2 
17.0 


24.2 
15.0 


4.6 
13.4 


1.4 
25.6 


2.1 
3.0 


5.6 


19 




5.0 


20 


Cleaner slime tailings 








9.4 
38.8 


14.0 
15.5 


25.2 
3.8 


15.4 
14.2 


8.1 
22.1 


8.8 
16.8 


2.1 
.9 


3.4 


21 


Cleaner slime concentrate .... 


1.6 


22 


Combined concentrate 




















(9 + 13 + 15 + 21) 


40.3 


15.4 


3.7 


14.0 


21.8 


46.2 


2.1 


4.2 



48 



KEY 

(T) Product streom, 

see table 2 



Laterite leach residue 



Attritioner 



65-mesh screen 



Hydrocyclone 



J 

Reject 



Rougher low-intensity magnetic separator 



Reject 



Magnetic product 

Demagnetizer 
Scavenger low-intensity magnetic separator 



Nonmagnetic 
product 



Nonmagnetic 



product 



@ 



? 



Screw classifier 



Reject 



Rougher sand table 



Thickener 



Rougher slime table 



Scavenger sand table 



Reject 




Bartles-Mozley concentrator 



Scavenger slime table 



Reject Reject 



Chromite concentrate 



FIGURE 4.— Chromite from pilot plant leach residues. 



49 



SUMMARY AND CONCLUSION 



Southern Oregon and northern California laterites are 
potentially a significant domestic resource of Ni, Co, and Cr. 
Recovery of the Ni and Co by a hydrometallurgical process 
developed by the Bureau was successfully demonstrated at 
several operating scales. In an attempt to recover the Cr 
values from the laterite, a scheme was devised and 
perfected for capturing chromite from either the 
hydrometallurgical residue or the untreated laterite by stan- 
dard mineral dressing procedures. The preferred beneficia- 
tion feed is the residue after Ni and Co have been removed, 
because it is already ground and in a slurry form that is 
readily transported to the chromite beneficiation circuit. 

Recoveries of up to 50 pet and concentrate grades of 35 
to 40 pet Cr 2 3 can be expected from a simple beneficiation 
procedure, which includes sizing plus magnetic and gravity 



separation. The low recovery and the low grade of concen- 
trates can be attributed to the fine particle size of both the 
chromite and the gangue. The chromite contained in many 
of the laterite deposits has a relatively low Cr 2 3 content 
and Cr-Fe ratio; this is a limiting factor in concentrate 
grades. 

Chromite concentrates recovered from laterites by the 
Bureau processing technology have been used in research 
on developing technology for pyrometallurgical preparation 
of ferrochromium and for fusion-leaching as a path to Cr 
chemicals or high-purity metal. The fine size of the 
recovered chromite concentrate makes it particularly 
suitable for preparation of Cr chemicals. Research on both 
of these processing approaches is described in detail later in 
this publication. 



REFERENCES 



1. Thayer, T. P. Chromium Ch. in U.S. Mineral Resources. U.S. 
Geol. Surv. Prof. Paper 820, 1973, pp. 111-121. 

2. Rice, W. L. Pacific Northwest Nickel Laterites -BuMines In- 
vestigations 1943-1980. Pres. at Pac. NW Metals and Min. Conf., 
AIME, Portland, OR, Apr. 27-29, 1981, 8 pp.; available upon re- 
quest from R. E. Siemens, BuMines, Albany, OR. 

3. Siemens, R. E., and J. D. Corrick. Process for the Recovery of 
Nickel, Cobalt, and Copper from Domestic Laterites. Min. Congr. 
J., v. 63, No. 1, 1977, pp. 29-34. 



4. Kirby, D. E., D. R. George, and C. B. Daellenbach. Chromium 
Recovery From Nickel-Cobalt Laterite and Laterite Leach 
Residue. BuMines RI 8676, 1982, 22 pp. 

5. Minerals Science Division, UOP Inc. New Procedure for 
Recovering Nickel and Cobalt From Western Laterites. Economic 
Feasibility (contract J0285021). BuMines OFR 68-82, 1982, 169 
pp.; NTIS PB 82-245945. 



BuMines IC 9087: Chromium-Chromite: Bureau of Mines Assessment and Research 



51 



CHARACTERIZATION AND BENEFICIATION OF DOMESTIC 
CHROMITE-BEARING MATERIALS 

By Lawrence L. Brown 1 



ABSTRACT 



The Bureau of Mines performed characterization and 
beneficiation studies on materials from domestic chromite- 
bearing deposits in order to more completely evaluate 
potential resources of this critical and strategic mineral. In 
cooperation with the Bureau's Field Operations Centers, 
which performed reconnaissance studies on deposits, bulk 
samples were obtained for mineralogical, physical, 
chemical, and concentration studies at the Albany Research 
Center to properly characterize the deposits. 

Representative specimens were selected from the 
samples for mineralogical studies including polished sur- 
face, optical and scanning electron microscopy, electron 
microprobe examination, magnetic separation, and libera- 
tion determination. A beneficiation procedure that included 



grinding, sizing, and gravity concentration was developed 
to produce chromite concentrates. Beneficiation charac- 
teristics, grade, general recovery, and classification of the 
chromite concentrate were determined. 

Chromite is not a simple mineral but a series of mineral 
varieties within a larger grouping of minerals called spinels. 
The Cr 2 3 content of "chromite" has been found to range 
from 15 to 64 pet. The traditional classification system 
based on usage (metallurgical, chemical, and refractory 
grades) for rating quality specifications is no longer ade- 
quate, and a more suitable terminology has been proposed 
and used: high-Cr, high-Fe, and high-Al chromites. Two new 
categories, marginal and submarginal chromite, are 
presented for rating chromite concentrates. 



INTRODUCTION 



Chromites in domestic deposits were characterized by 
mineralogical and benefication studies in an effort to 
facilitate possible utilization of this critical and stragetic 
mineral now or at some future date. In cooperative efforts 
with the Bureau's Alaska Field Operations Center (AFOC) 
and Western Field Operations Center (WFOC), bulk 
samples were selected from chromite-bearing areas in the 
field and forwarded to the Albany Research Center (ALRC) 
for these studies. Additional sample materials were ob- 
tained from State and private sources as the opportunity 
arose. 

Field office personnel conducted reconnaissance in- 
vestigations, studied and analyzed the geologic nature of the 
chromite-bearing deposits, and evaluated deposits from a 
resource standpoint including estimates of the potential ton- 
nage of chromite available. Mineralogical and beneficiation 
information is a very important part of these evaluations in 
that the mineralogical, chemical, and physical character and 
the crushing, liberation, and recovery characteristics bear 
strongly on deposit evaluation. 

In the last 6 years the Bureau has focused on studies of 
chromite resources in Alaska and has completed six reports 



(1-6). The publications describe chromite occurrences in 
Alaska and, except for possible new discoveries, represent a 
significant contribution to the Bureau's studies of chromite 
deposits in that State. A comprehensive summary report is 
being compiled. 

The studies are, of necessity, not overly detailed in 
either geology or characterization, as the degree of detail 
required for such studies is beyond the scope of the Bureau's 
program. The amount of data provided will, however, give 
the Nation's decision and policy makers a realistic view of 
the resources available and of the nature of the chromite in 
Alaskan deposits, and enable more rapid future develop- 
ment of the deposits in time of possible national need. 



■Group supervisor, geologist, Albany Research Center, Bureau of Mines, 
P.O. Box 70, Albany, OR 97321. 





Abbreviations Used in This Paper 


°c 


degree Celsius 


ft 


foot 


in 


inch 


lb 


pound 


^m 


micrometer 


pet 


weight percent 



52 



CHROMITE: THE MINERAL 



The theoretical composition of chromite, a spinel group 
mineral, is Fe 2 *Cr 2 4 . This composition is only approached 
in chromite found in meteorites. Chromite is more accurate- 
ly referred to as an isomorphous solid solution of con- 
tinuously variable composition (Fe 2 *,Mg)(Cr,Al,Fe 3 *) 2 4 . 
This wide compositional variation can best be illustrated by 
the fact that the chromium oxide (Cr 2 3 ) content in 
"chromite" has been found to range from 15 to 64 pet. 
(Theoretical chromite would contain 67.9 pet.) Consequent- 
ly, the physical and chemical properties of "chromite" from 
different deposits and even within single deposits may vary 
widely. This is the major reason for the differences in the 
mineral's response to beneficiation and metallurgical proc- 
essing and, ultimately, in its end use. 

A discussion of the spinel group is in order to help 
clarify the wide compositional variations noted in chromite. 
The group consists of three series of minerals with the 
general formula AB 2 X 4 (where A = Mg, Fe 2 *, Zn, Mn, Ni; 
B = Al, Cr, Fe 3 *, Mn 3 *, V, Ti; X = 0)-the spinels [(Mg, 
Fe 2+ , Zn, Mn)(Al, Fe 3 *, Cr, Mn 3 *, V, Ti) 2 4 ], the magnetites 
[(Fe 2 *, Mg, Zn, Ni)(Fe 3 *, Al, Cr, Mn 3 *, V) 2 4 ], and the 
chromites [(Fe 2 *, Mg)(Cr, Al, Fe 3 *) 2 4 ] - with each of the 
minerals containing a number of well-defined mineral 
varieties. There is complete miscibility of components 
within series but much less between series. Pure end 
members are rarely found. The spinels do not commonly 
show wide variations in the B part of the formula. The series 
is incompatible with quartz. Mineral specie names are 
designated by the predominant divalent and trivalent 
atoms, and the substitutional varieties by the next most 
common constituent in order. Historic names also prevail. 
For example, the spinel hercynite (FeAl 2 4 ), with signifi- 
cant amounts of Mg and Cr substituted for Fe and Al, 
respectively, may be termed a magnesian chromohercynite. 
The Cr-bearing spinel-group minerals and mineral varieties 
of particular concern follow: 

Spinel (MgAl 2 4 ). -Forms a continuous replacement 
series with hercynite (FeAl 2 4 ) and with rnagnesiochromite 
(MgCr 2 4 ). Chromian spinel, containing a large proportion 
of Cr substituting for Al, has been called picotite, but 
picotite is now restricted to an intermediate variety, 
(Mg,Fe 2 *) (Al,Cr) 2 4 , with Al greater than Cr and with an 
Fe-Mg ratio of 3. 

Chromite (Fe 2 *Cr 2 4 ). -Forms a series with rnag- 
nesiochromite (MgCr 2 4 ) and hercynite (FeAl 2 4 ). Ordinary 
rnagnesiochromite usually contains some Fe 2 * substituting 
for Mg. With additional substitution it grades to ferroan 
rnagnesiochromite, the most common variety, and then to 
chromite. Aluminian rnagnesiochromite has Al substituting 
for Cr with a usual increase in Mg content. Additionally, 
Fe 3 * can substitute for Cr, giving a ferrian rnagnesio- 
chromite. It has been suggested that, since the majority of 



the members of the chromite series have Mg> Fe 2 *, the Mg- 
bearing variety is the normal chromite and that the end 
member Fe 2 *Cr 2 4 should be called ferrochromite. 

Magnetite (Fe 2 *Fe 3 * 2 4 ). - There is no Cr-bearing series 
to magnetite. However, Cr can substitute for Fe 3 * in 
magnetite in generally small amounts. Relatively large 
amounts of Cr in magnetite indicate admixed chromite 
mineral. 

Most Cr-bearing spinels also contain small amounts of 
Si0 2 and traces of other components such as Mn, Ti, and Ca. 
It has been found that there is generally a relationship be- 
tween the composition of a chromite and that of its enclos- 
ing rock. 

In the above discussion, considerable use has been made 
of volume 2 of Dana's System of Mineralogy, 7th Edition (7), 
and of volume 5 of Rock Forming Minerals (8). The reader is 
referred to these publications for further detailed informa- 
tion. 

The three traditional end use varieties or general grades 
of chromite have been metallurgical, chemical, and refrac- 
tory grades. However, technological advances during the 
last decade or so are now allowing considerable inter- 
changeability among these grades. Thus, the current, more 
definitive chromite classification that is preferred is- 

High-Cr chromite- A minimum of 46 pet Cr 2 3 with Cr- 
Fe ratio 2 (metallurgical grade). 

High-Fe chromite -40 to 46 pet Cr 2 3 with Cr-Fe ratio 
1.5 to 2.0 (chemical grade). 

High-Al chromite -More than 20 pet A1 2 3 and more 
than 60 pet A1 2 3 + Cr 2 3 (refrac- 
tory grade). 

Continued advances in chromite-use technology and im- 
provements in ore beneficiation and chromite upgrading 
science will undoubtedly lead to additional classification and 
specification changes. In the current characterization 
studies, two classifications were added to those listed above 
for evaluation and rating of chromite concentrates obtained 
from samples during the studies: 

Marginal chromite. -Material that meets either the 
grade or Cr-Fe ratio requirements for one of the above 
classifications and very nearly meets the other. 

Submarginal chromite. -Material that fails to meet the 
above classifications. 

These materials could be upgraded by developing 
technology to meet one or more of the preferred grade 
specifications; otherwise, industrial developers could pro- 
vide new markets to utilize these materials. 

For more detailed information on chromium and a 
general overview of the commodity, the reader is referred 
to recent Bureau of Mines publications (9-10). 



MINERALOGICAL CHARACTERIZATION 



The geological occurrence of chromite is almost entirely 
limited to igneous rock types high in Mg and Fe that are 
referred to as ultramafic rocks, mafic rocks, basic igneous 
rocks, or perioditites, and the serpentine and basic 
metamorphic rocks that have been derived from them. 



Sedimentary rocks and alteration materials derived from 
these rocks often contain significant amounts of 
weathering-resistant chromite. 

Ultramafic rocks originate in the mantle or deep in the 
earth's crust and are rare in the upper crust. They generally 



53 



are found at or near continental margins in the vicinity of 
plate-tectonic subduction zones and deep-seated interplate 
fractures. The Bushveldt Complex in Africa, an area of 
mafic rocks, is an exception. It is in a stable area of very old 
rocks and contains the bulk of the world's chromite 
reserves. 

Ultramafic rocks and peridotites contain less than about 
45 pet Si0 2 , are generally dark colored, and have a high 
specific gravity. They are rather simple mineralogically, be- 
ing composed primarily of olivine [(Fe,Mg) 2 Si0 4 ] and the 
pyroxene minerals enstatite (Mg 2 Si 2 6 ) and diopside 
(CaMgSi 2 6 ). The percentage of each mineral in any rock 
may vary from one extreme to the other. Small to large 
amounts of serpentine, other pyroxene minerals, amphibole 
minerals, and their alteration products chlorite, talc, and 



iron oxide minerals also may be present. Sulfides of Fe, Cu, 
and Ni also may be present in small to locally large amounts, 
along with trace to very minor amounts of the platinum- 
group minerals (PGM's). Chromite generally occurs in rock 
types high in olivine or in serpentine that has been derived 
from olivine. 

Chromite and magnetite are found in minor to abundant 
amounts in ultramafic rocks as very fine to coarse grained 
disseminations and intergrowths and locally as coalescent 
streaks and small to large lenses. Also, small to very large 
pods and continuous layers up to several feet thick of essen- 
tially pure chromite are found. Most domestic chromite pro- 
duction has come from larger pods and continuous layer 
deposits. 



SAMPLE MATERIALS 



In order to collect bulk samples with a chromite content 
sufficient for metallurgical testing, high-grade rock samples 
were intentionally selected from surface exposures, or 
specimens were collected from high-grade portions of 
sampling channels by personnel from AFOC and WFOC. At 
ALRC representative specimens were selected from each 
sample for mineralogical examination and characterization. 
The rest of the sample was reduced in size in a series of 
crushing steps to pass 1/4 in, and a head sample and samples 
for beneficiation tests were prepared. The head sample was 
pulverized and subjected to chemical analysis. 

The representative specimens were examined under a 
binocular microscope for preliminary description and 
mineral identification. Portions were selected for encapsula- 
tion in plastic resin for polished surface preparation so that 
studies by reflected light microscopy, scanning electron 
microscopy (SEM), and electron microprobe could be made. 

Detailed mineralogical examinations and liberation 
studies were made on samples split from sized fractions 
prepared from benefication feed and product materials. The 
sized products were separated on a laboratory-model 
isodynamic magnetic separator, and the resulting fractions 
were studied critically by petrographic methods. Mineral 
percentages based on weight were estimated, and high- 
purity chromite concentrates that best represented the 
chromite in the sample were prepared from gravity concen- 
trates by carefully controlled magnetic separation and then 
subjected to analysis. 

Composition of individual chromite grains was deter- 
mined by SEM and electron microprobe examination of 
polished surfaces. Associated mineral varieties were also 
analyzed, and the sample was scanned for lesser but impor- 
tant elements such as Ni, Cu, Au, and the PGM's. It has 
been observed that chromite from a particular locality 
usually has about the same character and chemical composi- 
tion and that the composition changes little across a grain. 

Compositional zoning in the chromite is seen, but is not 
common. Quite frequently, chromite will show late-stage 
magnetite that crystallized later than chromite from the 
magma; this magnetite is intimately associated on outer sur- 
faces and penetrates fractures in the chromite crystals. 
Where the crystals are highly fractured and separated, the 
magnetite may penetrate throughout the grain. An example 



of such crystallization is shown in figure 1, which displays 
electron microprobe micrographs and element distribution 
maps of typical grains from a magnetic product of a minus 
65-mesh chromite gravity concentrate. The sample is from 
Miners Point on Kodiak Island, Alaska. The central grain 
contains a core of chromite with a magnetite overgrowth 
and with olivine gangue attached. Other similar grains will 
be observed, as will the presence of intergrown, fine- 
grained magnetite in the gangue minerals. Liberation is not 
complete. The variable brightness that the element displays 
is an indication of the relative amounts of the element 
present. 

Examination of all the chromite-bearing products in this 
sample showed that most, if not all, chromite grains have 
magnetite overgrown on their surfaces and that the 
thickness of the overgrowth varies considerably from grain 
to grain, but the total amount of magnetite is not large, the 
Fe and Cr contents of the chromite are relatively uniform 
within grains and from grain to grain. Composition is about 
45 pet Cr 2 3 , 19 pet FeO, 15 pet A1 2 3 , and 13 pet MgO. 

Another interesting example of complicated 
mineralogical association is shown in figure 2, which 
displays SEM micrographs at two different magnifications 
of a polished surface specimen of chromite. The sample is 
from Dust Mountain in the Tonsina District, southern 
Alaska. SEM examination revealed that this sample's 
"chromite" is a magnesian chromohercynite containing a 
relatively large amount of exsolved chromian magnetite 
within grains and along grain boundaries. The white phase 
is the chromian magnetite. The hercynite contains about 25 
pet Cr 2 3 , 35 pet FeO, 28 pet A1 2 3 , and 10 pet MgO. The 
magnetite phase contains 75 pet Fe 3 4 , 18 pet Cr 2 3 , 3 pet 
A1 2 3 , 2.5 pet Ti0 2 , and 1.5 pet MgO. In the system 
magnetite-hercynite, a complete solid solution exists above 
858° C. 

The rock sample from which the above material came 
also contained massive magnetite and massive chromite; 
however, the chromite was borderline (marginal chromite) 
in grade with a high-purity concentrate containing only 40 
pet Cr 2 3 . The head sample contained 17.7 pet Cr 2 3 , and a 
minus 65-mesh magnetic concentrate contained 22.9 pet 
Cr 2 3 . 



54 




Specimen 



Chromium 




Silicon 



Aluminum 



FIGURE 1.— Electron microprobe micrographs and element distribution maps showing magnetite overgrowth 
on chromite grains. Grids are 33 /im square. 



55 



/ 



jff 






1 



• 



.% "^"*^f % 






< t 




>»%»*• 

#♦•* v 



*•»•• 



FIGURE 2.— SEM micrographs showing chromian magnetite (light gray) exolved from chromian hercynite (dark gray) 
within grains and along grain boundaries. A, x 90; S, x 1,000. 



BENEFICIATION 



The bulk samples contained fragments up to 12 in. in the 
largest dimension; as described earlier, each sample was 
crushed in a series of crushing operations to pass 1/4 in, and 
then a head sample and 20-lb sample splits for beneficiation 
tests were prepared. Care was required in crushing and 
milling because chromite, by nature, is brittle and will 
reduce in size rather rapidly. In addition, both the chromite 
and the gangue minerals, especially olivine, usually are 
highly fractured, as observed under the microscope, and 
therefore will crush rather easily. Without care and control, 
excessive amounts of slime-sized particles are produced. 
The general beneficiation procedure developed to concen- 
trate the chromite from the samples is shown in figure 3. 
The procedure was modified to suit individual samples. 

In preparation for beneTiciation studies, a presplit 20-lb 
sample was sized at 28 and 65 mesh. The plus 28-mesh frac- 
tion was stage-ground dry to pass 28 mesh and sized on a 
65-mesh screen. The minus 28- plus 65-mesh fraction was 
beneficiated on a sand deck of a 2- by 4-ft laboratory shaking 
table to produce a clean gravity concentrate and tailings. 
The tailings were dried and then stage-ground to minus 65 
mesh, combined with the minus 65-mesh material from the 
initial grinding and screening, and beneficiated on a slime 
deck. A high-grade concentrate, middlings, coarse tailings 
(those that settled and banded on the table), and slime tail- 
ings (those that washed off the deck before they had a 
chance to settle) were collected. A scavenger tabling opera- 
tion was done on the middling product to improve chromite 
recovery. Commonly, on high-grade samples, there was an 
overlap between the middlings and course tailings, and sub- 
stantial amounts of chromite were observed intermixed 
with the coarse tailings in overlapping bands on the table. 
When this happened, the products were combined and given 
a scavenger tabling. When the samples contained fine- 
grained chromite or were very low grade, the entire sample 
was ground to minus 65 mesh and rougher and cleaner ta- 
bling was done rather than the rougher-scavenger sequence. 



All of the concentrates produced were classified according 
to the system presented earlier. 

Examples of beneficiation results on bulk sample 
materials collected from three widely separated areas in 
Alaska are presented below. The results show the variability 
of chromite and the variability of results that may be ex- 
pected from deposits in any one area. Thirty-five samples 
were collected from chromite deposits along the Border 



Bulk sample 
-*■ Crushers 



T 

■ Screens 



1/4 in +28 mesh -28 + 65 mesh -65 mesh 

Rodmill , » 



J I 

Concentrate Tailings 

* Rodmill 



■ 65 mesh 

J 



-65 mesh 

X 



Rougher slime table 



r 



Concentrate Middlings 

_ I 

Scavenger slime table 

I I 



} 1 

Coarse tailings Slime tailings 



Concentrate 



FIGURE 3.— General beneficiation procedure used to con- 
centrate chromite from rock samples. 



56 



Ranges Fault in southern Alaska. Concentrates produced 
from these samples gave 24 high-Cr or marginal high-Cr 
concentrates, 6 high-Fe or marginal high-Fe concentrates, 
and 5 submarginal chromites. Chromite recoveries ranged 
from 37 to 95 pet, with Cr-Fe ratios ranging from 0.6 to 3.1. 

The highest grade concentrate contains 57.8 pet Cr 2 3 , 
and 17 concentrates have grades in excess of 50 pet Cr 2 3 . 
The highest Cr-Fe ratio obtained was 3.1, and 11 concen- 
trates have ratios of 2.5 or better. The five submarginal con- 
centrates were of low grade and low Cr-Fe ratio and could 
not be improved by further beneficiation. 

In a second example, 10 samples collected from low- 
grade deposits in the western Brooks Range, northwestern 
Alaska, were all high-Cr chromites. Concentrate grades 
produced ranged from 49 to 59.5 pet Cr 2 3 with Cr-Fe 
ratios from 2.3 to 3.3. Recoveries ranged from 72 to 99 pet. 

As a third example, 11 samples were collected from low- 
grade deposits in the Caribou Mountain and lower Kanuti 
River areas in central Alaska. Three samples produced high- 



Cr chromite concentrates, two produced high-Fe Concen- 
trates, and one produced a high-Al chromite concentrate. 
Three other samples produced marginal concentrates, and 
two produced submarginal concentrates. Chromite 
recoveries ranged from 54 to 92 pet with Cr-Fe ratios rang- 
ing from 0.8 to 2.4. The highest grade concentrate con- 
tained 53.8 pet Cr 2 3 with a Cr-Fe ratio of 2.4. 

Magnetic separation as a beneficiation step was con- 
sidered and may be suggested by sample mineralogy, but 
generally improved Cr grade and Cr-Fe ratio would be at 
the expense of chromite recovery. High-Fe chromites are 
more magnetic than high-Cr chromites. Likewise, elec- 
trodynamic separation was considered, and while good 
products could be recovered, the process is time consuming 
and throughput rate is slow. 

Other steps such as flotation or the closer sizing of 
gravity separation feed materials could have been taken to 
possibly improve grade, Cr-Fe ratio, and recovery, but such 
steps were beyond the scope of these studies. 



SUMMARY AND CONCLUSIONS 



In cooperation with Bureau of Mines Field Operations 
Centers, State departments of geology, and others, bulk 
samples of chromite-bearing materials were received from 
domestic deposits in Alaska and the Northwest. The 
samples were subjected to characterization and beneficia- 
tion studies to provide data for more complete resource 
evaluation for this strategic and critical mineral. 

The mineralogical nature of "chromite" was discussed. 
Chromite is not a simple mineral but a series of mineral 
varieties within a larger grouping of minerals called spinels. 
The material referred to as chromite has a wide composi- 
tional variation in Cr 2 3 content ranging from 15 to 64 pet, 
although the mineral from a single deposit is usually of 
uniform composition. The classification scheme used to rate 
quality specifications for chromite usage was discussed, 
and, as promoted by many experts in the field, a more ap- 
propriate terminology for classification of high-Cr, high-Fe, 
and high-Al chromite is favored. Two new classifications, 
marginal and submarginal chromite, were suggested for ad- 
dition to the above ratings for evaluation and rating of 
chromite concentrates. 



The geological occurrence and mineralogical content of 
chromite-bearing rock were discussed. Representative 
specimens were selected for various mineralogical studies 
including polished surface preparation, optical and scanning 
electron microscopy, electron microprobe examination, 
magnetic separation, and liberation determination. Mineral 
content percentage estimates were made, and chemical 
analyses were performed. Examples of the mineralogical 
character of selected chromite variations were discussed 
and illustrated. 

A beneficiation process that included grinding, sizing, 
and gravity concentration was developed to produce 
chromite concentrates from the samples. Other beneficia- 
tion procedures were examined and evaluated, but they 
generally were less successful than the scheme designed in 
recovering chromite from the sample materials studied. The 
studies described were not designed to determine optimum 
chromite recovery of any one particular sample, but rather 
to determine beneficiation character, grade, general 
recovery, and classification of the chromite minerals pro- 
ducible from the deposits. Examples are given on samples 
from three different areas in Alaska. 



REFERENCES 



1. Foley, J. Y., and M. M. McDermott. Podiform Chromite Occur- 
rences in the Caribou Mountain and Lower Kanuti River Areas, 
Central Alaska. Part I: Reconnaissance Investigations. BuMines IC 

8915, 1983, 27 pp. 

2. Dahlin, D. C, L. L. Brown, and J. J. Kinney. Podiform 
Chromite Occurrences in the Caribou Mountain and Lower Kanuti 
River Areas, Central Alaska. Part II: Beneficiation. BuMines IC 

8916, 1983, 15 pp. 

3. Foley, J. Y. Chromite Deposits Along the Border Ranges 
Fault, Southern Alaska. Part I: Reconnaissance Investigations. 
BuMines IC 8990, 1985, 58 pp. 

4. Dahlin, D. C, D. E. Kirby, and L. L. Brown. Chromite 
Deposits Along the Border Ranges Fault, Southern Alaska. Part 2: 
Beneficiation. BuMines IC 8991, 1985, 37 pp. 



5. Foley, J. Y., T. Hinderman, D. E. Kirby, and C. L. Mardock. 
Chromite Occurrences in the Kaiyuh Hills, West Central Alaska. 
BuMines OFR 178-84, 1983, 20 pp; NTIS, PB 85-106219. 

6. Foley, J. Y., J. C. Barker, and L. L. Brown. Critical and 
Strategic Minerals Investigations in Alaska: Chromium. BuMines 
OFR 97-85, 1985, 54 pp. 

7. Plache, C, H. Berman, and C. F. Frondel. Dana's System of 
Mineralogy. Wiley, 7th ed., v. 1, 1944, pp. 678-712. 

8. Deer, W. A., R. A. Howie, and J. Zussman. Rock Forming 
Minerals. V. 5, Nonsilicates. Wiley, 1962, pp. 56-88. 

9. Papp, J. F. Chromium. BuMines Mineral Commodity Profile, 
1983, 21 pp. 

10. . Chromium. Ch. in Mineral Facts and Problems, 1985 

Edition. BuMines B 675, 1985, pp. 139-156. 



BuMines IC 9087: Chromium-Chromite: Bureau of Mines Assessment and Research 



57 



FLOTATION BENEFICIATION OF CHROMITE FROM LOW-GRADE 

DEPOSITS 

By J. L Huiatt 1 



ABSTRACT 



The Bureau of Mines investigated conventional flotation 
techniques for upgrading chromite samples from the Mouat 
and Benbow Mines in the Stillwater Complex, Nye, MT, and 
in low-grade California chromite samples. A newly devised 
column flotation technique was also investigated. 

Deslimed Mouat samples were upgraded satisfactorily 
by conventional flotation with HF depressant and oleic acid 
collector but were not upgraded satisfactorily when floated 
with a primary amine collector. The poor upgrading was at- 
tributed to the presence of olivine, which floated with 
chromite. Deslimed Benbow samples responded favorably 
to both flotation techniques; however, amine flotation pro- 



duced higher recoveries. Flotation of undeslimed Benbow 
samples with carboxymethylcellulose and tall oil, or with an 
oil emulsion, produced acceptable-grade chromite concen- 
trates but at reduced recoveries. Beneficiation of low-grade 
California chromite samples by these four procedures was 
not satisfactory. 

A column flotation apparatus, which can use either 
coarse or fine air bubbles for frothing, was constructed and 
evaluated using the amine flotation technique. Results 
demonstrated that column flotation was superior to conven- 
tional flotation for beneficiating either deslimed or 
undeslimed Benbow chromite ore samples. 



INTRODUCTION 



Gravity separation techniques have been quite effective 
in beneficiating domestic chromite resources. For example, 
from 1952 to 1961 the American Chrome Co. used tabling to 
upgrade ore from the Mouat and Benbow Mines in the Still- 
water Complex, Nye, MT, from about 22 to 41 pet Cr 2 3 . 
Nearly 1 million st of chromite concentrate having a Cr-Fe 
ratio of 1.7 was produced (1). Tabling was also used to con- 
centrate chromite at the Pilliken Mine near Auburn, CA, 
and the Grey Eagle Mine in Glenn County, CA. The Hum- 
phreys spiral is also quite effective in beneficiating chromite 
ores, although tabling may produce somewhat higher 
grades and recoveries. 

Particle size limits the use of gravity separation tech- 
niques such as tabling and Humphreys spiral separation. 
The lower particle size limit is approximately 100 mesh. 
However, smaller particle sizes can be beneficiated on tables 
with slime decks or on a Bartles-Mozley cross-belt separa- 
tor; these techniques have lower production capacities. 
Many domestic chromite deposits are low grade and finely 
disseminated; consequently, liberation of the bulk of the 
mineral values may require grinding through 100 mesh, 
often precluding gravity beneficiation. 

Froth flotation offers an alternative technique for bene- 
ficiating lower grade deposits where fine grinding is 
necessary for liberation. Flotation can be used in concert 
with gravity methods or by itself. Generally flotation is ef- 
fective in upgrading mineral values ranging from minus 35 
mesh to about 20 ^m in size. Occasionally the flotation tech- 
nique can be modified to treat feed materials that are slight- 
ly coarser and slightly finer than the above size range. 
Flotation has found limited commercial use for upgrading 
domestic chromite ores. The most recent commercial use of 
chromite flotation was at the Butler Estates property near 



Coalinga, CA; however, the mine was closed in 1976 
because of economic factors. 

Considerable work has been performed by the Bureau of 
Mines and other laboratories to investigate chromite flota- 
tion behavior and to devise flotation techniques for low- 
grade domestic ores (2-8). The techniques were designed to 
overcome problems inherent to a particular ore body. Col- 
lectively, the problems include (1) need of fine grinding to 
liberate chromite values, (2) presence of abundant minus 
20-^m slimes, (3) aging of chromite and gangue minerals, 
and (4) nonselectivity due to natural or induced activation of 
gangue and chromite mineral values. 

Slimes present chronic problems with most domestic 
chromite ores. These ores are low grade and finely dissemi- 
nated and require considerable grinding to liberate chromite 
minerals; consequently, excessive slimes are generated. The 
slimes are detrimental to froth flotation because they may 
(1) form a fine coating on the mineral particles, preventing 
selective reagent adsorption and hence depressing flotation 
or decreasing mineral selectivity, (2) consume excessive 
quantities of reagents, and (3) decrease the flotation rate by 
increasing pulp viscosity. The most expedient method for 
resolving the slimes problem is to deslime prior to flotation; 
however, the desliming results in significant chromite 
losses. 



'Research supervisor, Salt Lake City Research Center. Bureau of Mines, 
729 Arapeen Drive, Salt Lake City, UT 84108. 





Abbreviations Used in 


This 


Paper 


ft 


foot 






in 


inch 






lb/st 


pound per short ton 




min 


minute 






nm 


micrometer 






pet 


weight percent 






St 


short ton 







58 



A variety of gangue minerals are associated with 
chromite ores including quartz, olivine, serpentine, diopside, 
hedenbergite, chlorite, labradorite, biotite, enstatite, 
calcite, magnetite, bronzite, epidote, and hematite. Fibrous 
minerals may also be present. The presence and relative 
abundance of the minerals varies markedly with the ore 
body. Many factors influence the floatability, or nonfloata- 
bility, of gangue minerals as well as the chromite minerals. 
These factors include, but are not limited to, pulp pH, 
mineral solubility, presence of metallic ions in flotation 
water, types of reagents added, and the history of the ore 
being treated (9-11). 

In a fundamental study, Smith (11) determined that 
floatability of naturally occurring chromite depended on 
whether the mineral was aged in air and whether the 
mineral had been heated. The observed effects were at- 
tributed to oxidation and reduction reactions involving sur- 
face chromium and iron species. Acid washing removed 
easily soluble surface material; thus, after washing, the 
mineral behaved like a simple oxide and was floatable with 
anionic or cationic collectors, depending on pH. 

Smith also reported that among the gangue minerals 
studied (olivine, diopside, hedenbergite, and bronzite), 
olivine appeared to be the most readily floated and was the 
mineral most likely to cause problems in the chromite flota- 
tion system. All minerals appeared to be affected in their 
electrokinetic, adsorption, and flotation behavior by metal 
ions that dissolve naturally from chromite ore. Aging of 
stockpiled ore will probably change its flotation character- 
istics. 

Metallic ions, whether originating from the chromite 
mineral or present naturally in the flotation water, are likely 
to affect chromite and gangue mineral flotation. The 
theoretical composition of chromite is FeOCr 2 3 , but in 
nature Mg* + is substituted for Fe", while Fe"* and Al* ++ are 
substituted for Cr** + . Fuerstenau and Palmer (9) reported 



that the composition has a direct effect on the electrokinetic 
properties of the mineral surface. For example, points of 
zero charge (PZC) at pH 4.4 to 9.6 have been measured for 
chromites of various compositions. The electrokinetic 
behavior is attributed to the presence of hydroxy ion 
species; i.e., Mg(OH) + and Fe(OH) + at pH 11 and 8, respec- 
tively. These are the pH values where zeta potential rever- 
sal occurs and where the hydroxy complexes are present in 
significant amounts. Fuerstenau and Palmer also reported 
that aluminum and chromium hydroxy species are not in- 
volved in chromite flotation. 

The flotation behaviors of chromite ores from several 
locations have been evaluated by the Bureau using several 
techniques. A basic flotation method was developed by 
Havens (3). The Havens method consisted of treating de- 
slimed pulp with sodium fluoride (NaF) and sulfuric acid 
(H 2 S0 4 ), followed by chromite flotation with oleic acid col- 
lector and Emulsol X-l dispersant. Samples of the 
Stillwater Complex ore (Mouat Mine), beach sands, and 
minus 200-mesh chromite slime tailings were reported to be 
amenable to this procedure. Flotation produced substantial 
upgrading at fair recoveries of the Mouat and beach sand 
samples. The slime tailings upgraded fourfold, but recovery 
was only 44.6 pet. Desliming of all three samples at 10-/im 
particle size was necessary to achieve the metallurgy 
reported. Reagent consumptions were high. For example, 
oleic acid consumption ranged from 1.1 to 5.8 lb/st, Emulsol 
X-l from 0.2 to 1.2 lb/st, H 2 S0 4 from 12.4 to 17.7 lb/st, and 
NaF from 6.4 to 16.5 lb/st. 

Because of high reagent consumptions and marginal 
grades and recoveries achieved using available flotation 
technology, the Bureau performed research to evaluate 
available technology and to devise new and improved 
methods for testing domestic chromite ores. This report 
summarizes work accomplished between fiscal years 1978 
and 1980 and current work. 



MATERIALS 



Principally, one Mouat and two Benbow Mine samples 
from the Stillwater Complex were used in the research. The 
samples were collected from ore piles at the mine sites. 
Table 1 lists the partial chemical analyses of these ore 
samples. The mineralogy of the two Benbow samples was 
similar. The most abundant silicate minerals were serpen- 
tine and enstatite; subordinate amounts of olivine and diop- 

TABLE 1.— Chemical analyses of Stillwater Complex samples, 
percent 



Analysis 


Benbow 1 


Benbow 2 


Mouat 


Cr 2 0, 


16.3 
11.6 

20.8 
23.0 
12.8 


20.4 
12.2 
21.0 
17.0 
11.6 


23.4 


Fe 

SIO, 


16.8 
17.0 


MgO 

Al 2 3 


16.0 
10.6 







side were present. The Mouat sample contained abundant 
olivine and enstatite with small amounts of serpentine, diop- 
side, chlorite, labradorite, and biotite. The chromite mineral 
from the Stillwater Complex contained about 46 pet Cr 2 3 
with a Cr-Fe ratio of less than 2. Liberation size was esti- 
mated, petrographically, to be about minus 48 mesh; how- 
ever, finer grinding was necessary to achieve optimum 
flotation. 

Samples ranging from 0.5 to 3.6 pet Cr 2 3 were ob- 
tained from deposits near Auburn, Seiad Creek, and Cres- 
cent City, CA. Collectively, the California samples con- 
tained olivine, antigorite serpentine, tremolite, epidote, 
enstatite, and chlorite. Liberation size was minus 48 mesh. 
The Cr 2 3 contents of the chromite minerals ranged from 
46 to 55 pet. The Cr-Fe ratio was not determined. 



CONVENTIONAL FLOTATION TECHNIQUES 



Chromite flotation separation from either deslimed or 
undeslimed Stillwater Complex samples was investigated 
using four flotation reagent schemes. Conventional 
laboratory flotation cells were used in the separations. A 
modified version of the Havens oleic acid-NaF method (in 
which HF was used instead of NaF) (3) and an amine 



method devised and patented by the Bureau (5-6) were used 
to beneficiate deslimed samples. Preliminary testing 
demonstrated that chromite samples were not amenable to 
the oleic acid-HF or the amine flotation procedures. Conse- 
quently, an oil emulsion method and a carboxymethyl- 
cellulose (CMC)-tall oil method (12) were used to beneficiate 



59 



undeslimed samples. Flotation screening tests were also 
performed on low-grade chromite samples from northern 
California to determine their amenability to the preceding 
flotation methods. 

FLOTATION PROCEDURES 

Petrographic analyses indicated that chromite in the 
Benbow and Mouat samples was liberated at minus 48 
mesh; however, optimum flotation occurred at screen sizes 
of minus 65 mesh or finer. Chromite in the California 
samples was liberated at minus 65 mesh; best flotation oc- 
curred at this grind size. 

Oleic acid-HF.- Minus 65-mesh Benbow 1 sample (16.3 
pet Cr 2 3 ) was deslimed by sedimentation and decantation 
according to Stoke's Law at 30-/tm particle size, conditioned 
at 25 pet solids with 3.0 lb/st HF, and floated at pH 4 in 
three 5-min rougher stages using 5.0 lb/st oleic acid total. 
Minus 100-mesh Benbow 2 (20.4 pet Cr 2 3 ) and Mouat (23.4 
pet Cr 2 3 ) chromite samples were deslimed at 20 ^m parti- 
cle size, conditioned at 25 pet solids with 2.0 lb/st HF, and 
floated at pH 4 in three rougher stages using 2.0 lb/st oleic 
acid total. Sulfuric acid was used to adjust pH. 

Amine. -Minus 65-mesh Benbow 1 sample was deslimed 
at 20-^m particle size and conditioned at 25 pet solids with 
H 2 S0 4 and primary coco-amine (Armac C). The pulp was 
floated in three 5-min rougher stages. Total reagent con- 
sumption was 33 lb/st H 2 S0 4 and 0.6 lb/st Armac C; flota- 
tion pH was 2. 

Minus 100-mesh Benbow 2 sample was deslimed at 
20-^m particle size, conditioned at 25 pet solids with H 2 S0 4 
and amine, and floated in two 5-min rougher and one 5-min 
cleaner stages. Total reagent consumption was 34 lb/st 
H 2 S0 4 and 1.0 lb/st Armac C. Flotation pH was 2. 

Minus 65-mesh Mouat samples was deslimed at 20-/tm 
particle size and conditioned at 25 pet solids with H 2 S0 4 and 
Armac C. The pulp was floated in two 5-min rougher stages 
and one 5-min cleaner stage. Total reagent consumption 
was 56 lb/st H 2 S0 4 and 0.8 lb/st Armac C. Flotation pH was 
2. 

Oil emulsion. -Minus 65-mesh Benbow 2 sample was 
conditioned (without prior desliming) at 60 pet solids and pH 
8 for 40 min with an oleic acid-diesel oil emulsion. The pulp 
was diluted to 25 pet solids and floated in one rougher and 
one cleaner stage. Total reagent addition was 4.0 lb/st oleic 
acid and 40 lb/st No. 2 diesel oil. Flotation time was 5 min 
per stage. Pulp was maintained at pH 8. 

CMC-tall oil. - Minus 65-mesh Benbow 2 sample was 
conditioned (without prior desliming) at 25 pet solids and pH 
11.3 with 1.0 lb/st dispersant [3 parts Na 2 Si0 3 to 1 part 
(NaP0 3 ) 6 ], 0.5 lb/st CMC, and 2.5 lb/st tall oil. The pulp was 
floated for 7 min. The rougher concentrate was further up- 
graded in a 9-min cleaner flotation stage using an additional 
0.5 lb/st CMC and 2.5 lb/st tall oil; flotation pH was main- 
tained at 11.3. 

The minus 65-mesh samples from the California de- 
posits were deslimed and treated by the four flotation 
methods described above. Conditions were similar, except 
reagent dosages were higher. 

CONVENTIONAL FLOTATION RESULTS 

Flotation results for the Benbow and Mouat samples are 
listed in table 2. Both Benbow samples responded well to the 
amine flotation method. Rougher flotation upgraded the 
16.3-pct-Cr 2 3 sample to 38.4 pet Cr 2 3 at 84-pct recovery. 



Rougher flotation followed by cleaner flotation upgraded 
the 20.4-pct-Cr 2 O 3 sample to 43.6 pet Cr 2 3 at 86-pct re- 
covery. Rougher flotation using HF and oleic acid upgraded 
the 16.3- and 20.4-pct-Cr 2 O 3 materials to 40.1 and 40.3 pet 
Cr 2 3 , respectively. However, chromite recoveries were 
only 75 pet and 60 pet, respectively. 

The HF-oleic acid method upgraded the 23.4-pct-grade 
Mouat sample to 39.6 pet Cr 2 3 at a rougher flotation 
recovery of 82 pet. Amine flotation recovered 94 pet of the 
chromite in rougher flotation and 84 pet in a cleaner flota- 
tion; however, only a 31.8-pct-Cr 2 3 concentrate was ob- 
tained even with cleaner flotation. 

The Mouat sample was not as amenable to amine flota- 
tion as the Benbow 2 sample. The main gangue mineral in 
the Mouat sample was olivine, which readily floated with the 
amine collector. The main gangue mineral in the Benbow 
sample was serpentine, which does not float readily with 
amine collector. The difference in gangue mineral constitu- 
ents probably accounts for the poor selectivity when floating 
Mouat chromite by the amine method. 

The CMC-tall oil and the oil emulsion methods, in which 
desliming was not done prior to flotation, produced 85- and 
83-pct-chromite rougher flotation recoveries, respectively, 
from the Benbow 2 sample; however, rougher concentrate 
grades were only 33 pet Cr 2 3 . The gangue mineral slimes 
present in the ore sample were not completely depressed, 
resulting in poor selectivity. Cleaner flotation of the 
rougher concentrates produced acceptable chromite grades 
of 38.6 and 41.4 pet Cr 2 3 , but chromite recoveries were 
reduced significantly. Total reagent consumptions were 
reasonable for the CMC-tall oil method but excessive for the 
oil emulsion method. 

Flotation of low-grade samples from Auburn, Seiad 
Creek, and Crescent City, CA, using the four flotation tech- 
niques achieved only limited success (table 3). The best re- 
sponse occurred when floating a deslimed Auburn sample 
using the HF-oleic acid reagent scheme; chromite was up- 
graded from 3.6 to 15 pet Cr 2 3 at 62-pct recovery. Oleic 
acid-HF flotation of the other samples containing less than 
3.6 pet Cr 2 3 consistently yielded poor-grade concentrates 

TABLE 2.— Chromite flotation from Benbow and Mouat 
samples, percent 





Rougher cone 


Cleaner cone 


Sample and 
flotation method 


CCA 
grade 


Distri- 
bution 


Cr 2 0, 

grade 


Distri- 
bution 


Benbow 1: 
HF-oleic acid . . . 


40.1 
38.4 

40.3 
40.8 
32.5 
32.9 

39.6 
28.8 


74.6 
84.4 

60.3 
89.1 
84.6 
83.2 

82.3 
94.0 


NA 
NA 

NA 
43.6 
38.6 
41.4 

NA 

31.8 


NA 

NA 


Benbow 2: 
HF-oleic acid .. . 


NA 
85.7 


CMC-tall oil 

OH emulsion .... 
Mouat: 
HF-oleic acid . . . 
Amine 


77.0 
68.8 

NA 

84.1 













NA Not analyzed. 



TABLE 3.— Oleic acid-HF flotation of low-grade California 
samples, percent 





Cr : 3 




Sample 


Head 

assay 


Cone 
grade 


Distri- 
bution 




3.6 

.5 

2.8 

1.0 


15.0 
1.5 
5.5 
1.4 


62.0 


Auburn (2) 

Crescent City 

Selad 


24.2 
50.3 
61.7 



60 



(1.5 to 5.5 pet Cr 2 3 ) at low recoveries (24 to 61 pet). Ex- 
cessive amounts of reagent were required (6 to 16 lb/st oleic 
acid). Beneficiation of the samples using amine, oil emul- 
sion, or CMC-tall oil reagent schemes was unsuccessful. The 



poor flotation response was attributed to slime particles, 
complex chromite mineralization, and nonselective reagent 
adsorption. Beneficiation of these samples could be achieved 
by gravity and magnetic separation techniques (13). 



NEW FLOTATION TECHNOLOGY 



The Bureau's Salt Lake City Research Center has been 
performing research on oxide mineral beneficiation. Initial 
efforts were directed toward devising reagent schemes for 
conventional flotation of oxide minerals. Flotation is diffi- 
cult because of complex mineralogy and abundant fine par- 
ticles. Satisfactory conventional methods, which produce ac- 
ceptable grades and recoveries with low reagent consump- 
tions, have not been developed; consequently, an investiga- 
tion of new flotation devices was initiated. As a result of this 
work, a flotation column was designed which utilizes coarse 
or fine bubbles to produce a mineralized froth. 

EQUIPMENT AND PROCEDURE 

The experimental column (fig. 1) is 2V2 in ID by 18 ft tall 
and is constructed of clear plexiglass tubing with Vi-in wall 
thickness. The column is equipped with injection and sam- 
pling ports located along its entire length. Coarse air bub- 
bles are introduced through fritted glass tubes mounted at 
the bottom and middle of the column. Fine air bubbles are 
produced extrinsically in a dissolved air generator and in-, 
jected through a slotted jet at the bottom of the column. 
Pulp conditioning is accomplished in a modified Denver cell; 
the pulp is then transported through tubing by gravity to an 
injection port located about 10 ft from the column bottom. 
Makeup water and wash water can be added at the column 
top or at any port along the column. Froth is collected in an 
annular launder at the top. Tailings can be recycled in the 
column or pumped to a scavenger column. 

Delimed and undeslimed Benbow 2 chromite samples 
were beneficiated in the column and by conventional flota- 
tion using the Bureau's amine flotation method. Minus 
65-mesh sample was conditioned for 10 min at pH 2.0 with 
2.0 lb/st Armac C. If appropriate, the ore was deslimed 
prior to conditioning at minus 20-/tm particle size, using up 
to 4.0 lb/st Na 2 Si0 3 dispersant. For deslimed samples, col- 
lector addition was reduced to 1.0 lb/st Armac C. The col- 
umn was partially filled with aerated water, to which 0.2 
lb/st Dowfroth 400 was added, and the conditioned pulp was 
introduced. When the pulp contacted the aerated water, a 
mineralized froth immediately developed. The froth moved 
up the column and was discharged. The tailings were re- 
cycled until all the chromite concentrate was collected. 
Flotation time was 4 to 6 min. Fine or coarse bubbles were 
used to develop froth. 

COLUMN FLOTATION RESULTS 

Table 4 compares results obtained by (1) conventional 
flotation in a Denver laboratory cell (conventional flotation 
results reported are those obtained concurrently with col- 
umn flotation results), (2) coarse bubble column flotation, 
and (3) fine bubble column flotation. Recovery results were 
based on analysis of samples as received. Conventional 
flotation of deslimed material recovered 77 pet of the 
chromite in a rougher concentrate containing 43.5 pet 
Cr 2 3 . Column flotation significantly improved chromite 
recovery and grade. For example, coarse bubble flotation 




FIGURE 1.— Flotation column (A) and bubble generator (8). 



61 



TABLE 4.— Amine rougher flotation of deslimed and undeslimed 

Benbow 2 chromlte using conventional flotation equipment and 

flotation columns, percent 



Flotation 


Cr 2 3 grade 


Distribution 


method 


Deslimed 


Undeslimed 


Deslimed 


Undeslimed 


Conventional 

Column: 

Coarse bubble . . 

Fine bubble 


43.5 

43.8 
44.7 


35.6 

41.6 
41.5 


77.0 

85.0 
87.1 


86.5 

94.3 
94.9 



recovered 85 pet of the chromite in a rougher concentrate of 
43.8 pet Cr 2 3 , and fine bubble flotation recovered 87 pet of 
the chromite in a rougher concentrate of 44.7 pet Cr 2 3 . 
Fine bubble column flotation appeared to be slightly better 
than flotation with coarse bubbles. 

Conventional flotation of undeslimed chromite was not 
satisfactory; the maximum grade was only 35.6 pet Cr 2 3 , 
and overall recovery was 87 pet. However, a marked im- 
provement in grade and recovery was achieved when bene- 



ficiating the material by column flotation using either coarse 
or fine bubbles. A 9-pct increase in recovery was attributed 
to flotation of chromite mineral in the slime fraction. 
Mineral particle separation occurred primarily in the pulp 
slurry rather than in the froth column; consequently, less 
gangue was occluded in the chromite froth, and higher 
grades were achieved. 

The advantages of using column flotation for bene- 
ficiating Benbow chromite sample with amine collector 
follow: (1) Desliming prior to flotation is not required; (2) 
flotation kinetics are improved; (3) extra cleaning steps are 
unnecessary; and (4) improved grades and recoveries are ob- 
tained. From a commercial consideration, flotation columns 
(1) require less space, e.g., one column has been used to 
replace two banks of conventional cleaner-flotation cells, (2) 
have fewer moving parts so that less maintenance is re- 
quired, (3) can be automated easily, and (4) have lower 
equipment and installation costs. 



SUMMARY AND CONCLUSIONS 



Four conventional flotation techniques were evaluated 
using Mouat and Benbow samples from the Stillwater Com- 
plex, Nye, MT, and low-grade samples from California 
chromite deposits. The techniques used oleic-HF, oil emul- 
sion, CMC-tall oil, and amine flotation reagent schemes. 

The Mouat sample (23.4 pet Cr 2 3 ) upgraded satis- 
factorily by flotation using HF depressant and oleic acid col- 
lector; however, it did not upgrade significantly using amine 
collector at acid pH, though recovery was high. For exam- 
ple, chromite upgraded to 39.6 pet Cr 2 3 at 82-pct recovery 
with HF-oleic acid scheme; amine flotation recovered 94 pet 
of the chromite in a rougher concentrate containing 28.8 pet 
Cr 2 3 . The low grade obtained using the amine collector 
was attributed to the presence of olivine, which cofloated 
with chromite. 

Both Benbow samples responded favorably to HF-oleic 
acid flotation and to amine flotation. Generally higher re- 
coveries were achieved using the latter reagent scheme. 

Flotation of undeslimed Benbow 2 sample (20.4 pet 
Cr 2 3 ) using CMC-tall oil or oil emulsion collectors produced 
rougher concentrates containing only 32.5 and 32.9 pet 
Cr 2 3 at recoveries of 85 and 83 pet, respectively. Flotation 
cleaning improved concentrate grade at significantly re- 



duced recoveries. Overall, amine flotation produced better 
chromite upgrading. 

A low-grade sample from Auburn, CA, upgraded from 
3.6 to 15.0 pet Cr 2 3 at 62-pct recovery using the HF-oleic 
acid method but did not respond favorably to the amine, oil 
emulsion, or CMC-tall oil flotation methods. Other low- 
grade samples, which contained less than 3.6 pet Cr 2 3 , did 
not respond favorably to any of the conventional flotation 
schemes. 

Column flotation of the Benbow 2 sample using coarse 
or fine air bubbles was investigated and compared with con- 
ventional flotation methods using a similar reagent scheme 
(Armac C collector). Results demonstrated that column 
flotation produced superior chromite concentrate grades 
and recoveries. Flotation kinetics was also improved. For 
example, in a single pass, column flotation of deslimed 
samples using coarse and fine bubbles produced concen- 
trates containing 43.8 and 44.7 pet Cr 2 3 at 85- and 87-pct 
recoveries, respectively. Column flotation of undeslimed 
samples produced concentrates containing nearly 42 pet 
Cr 2 3 at 94-pct recovery. Conventional flotation produced 
significantly lower grades and recoveries. 



REFERENCES 



1. Kingston, G. A., R. A. Miller, and F. V. Carrillo. Availability of 
U.S. Chromium Resources. BuMines IC 8465, 1970, 23 pp. 

2. Batty, J. V., T. F. Mitchell, R. Havens, and R. R. Wells. Bene- 
fieiation of Chromite Ores From Western United States. BuMines 
RI 4079, 1947, 26 pp. 

3. Havens, R. Froth Flotation of Chromite With Fluoride. U.S. 
Pat. 2,412,217, Dec. 10, 1946. 

4. Hunter, W. L., and G. V. Sullivan. Utilization Studies on 
Chromite From Seiad Creek, California. BuMines RI 5576, 1960, 
37 pp. 

5. Smith, G. E., J. L. Huiatt, and M. B. Shirts. Amine Flotation of 
Chromite Ores From the Stillwater Complex, MT. BuMines RI 
8502, 1981, 12 pp. 

6. Amine Flotation of Chromite From Acid Pulps. U.S. 

Pat. 4,311,584, Jan. 19, 1982. 

7. Sullivan, G. V., and W. A. Stickney. Flotation of Pacific North- 
west Chromite Ores. BuMines RI 5646, 1960, 14 pp. 



8. Sullivan, G. V., and G. F. Workentine. Beneficiating Low- 
Grade Chromites From the Stillwater Complex, MT. BuMines RI 
6448, 1964, 22 pp. 

9. Fuerstenau, M. C, and B. R. Palmer. Anionic Flotation of Ox- 
ides and Silicates. Ch. in Flotation, ed. by M. C. Fuerstenau. AIME, 
v. 1 (A. M. Gaudin Memorial Volume), 1976, pp. 148-196. 

10. Sagheer, M. Flotation Characteristics of Chromite and 
Serpentine. Trans. Soc. Min. Eng. AIME, Mar. 1966, 7 pp. 

11. Smith, R. W. Fundamentals of Chromite Flotation (grant 
G0274005, Univ. NV, McKay Sch. Mines). BuMines OFR 45-82, 
1981, 55 pp.; NTIS, PB 82-197492. 

12. Sher, F., M. Milosevic, and P. Bulatovic. Anionic Flotation of 
Chromite in an Alkaline Medium Without Preliminary Desliming. 
Mezhdunar. Kongr. Obogashch. Polez. Iskop. [Tr], 8th Congr., v. 1, 
1968, pp. 553-557 (Russ). 

13. Salisbury, H. B., M. L. Wouden, and M. B. Shirts. Bene- 
ficiation of Low-Grade California Chromite Ores. BuMines RI 
8592, 1982, 15 pp. 



BuMines IC 9087: Chromium-Chromite: Bureau of Mines Assessment and Research 



63 



A CHEMICAL METHOD FOR RECOVERING CHROMIUM FROM 

DOMESTIC CHROMITES 

By Gary L. Hundley 1 and R. S. Olsen 2 



ABSTRACT 



The Bureau of Mines has devised a procedure to recover 
Cr chemicals from low-grade domestic chromites. These 
domestic chromites contain Si and Al impurities at levels 
that are too high to permit processing by present industrial 
processes. The Bureau procedure consists of reacting 
chromite with molten NaOH under oxidizing conditions to 
form sodium chromate (Na2Cr0 4 ). The reaction product is 
leached with methanol to recover the majority of the 
unreacted NaOH, and then with water to remove the 
Na2Cr0 4 and the remainder of the NaOH. The Na2Cr0 4 pro- 
duct is recovered by evaporative crystallization from the 
aqueous solution. 



This report presents laboratory results of studies to 
determine the optimum fusion and leaching conditions and 
the Cr extractions obtained for several domestic chromite 
concentrates. Preliminary results on solution purification 
and crystallization are also included. The concentrates are 
from a variety of sources including the Stillwater Complex 
in Montana, Red Bluff Bay and the Kenai Peninsula in 
Alaska, and an Ni-Co laterite from southern Oregon. All of 
these concentrates were successfully treated by this pro- 
cedure. The best Cr extraction obtained for each of these 
materials ranged from 92.5 to 98.9 pet. 



INTRODUCTION 



Chromium is a commodity that is essential to the Na- 
tion's metallurgical, chemical, and refractory industries. 
The United States has no domestic production or economic 
reserves of chromite, the only commercial ore of Cr, and 
must rely on imports to meet national needs. The chemical 
industry uses approximately 25 pet of the chromite con- 
sumption for the production of pigments, chromic acid for 
plating and other chemicals used for leather tanning, wood 
preservatives, catalysts, and corrosion inhibitors (1). 

Commercial processes presently used to chemically 
treat chromite concentrates include an oxidizing roast of the 
chromite with Na2C0 3 and lime in a rotary kiln at around 
1,100° to 1,150° C. The amount of reagents and a diluent 
are controlled so that the reaction mixture remains as a 
solid phase in the kiln (2). Concentrates produced from 
domestic chromite deposits contain too much Si to be proc- 
essed by this method. The Si forms molten, sticky reaction 
products with the Na2C0 3 , which cause balls or rings of 
material to form in the kiln, hindering its operation, the Al 
content in domestic resources is also high, resulting in an 
excess consumption of reagents (3). 

A simplified flowsheet for the Bureau of Mines pro- 
cedure to recover Cr chemicals from low-grade domestic 
chromites is shown in figure 1. Briefly, the procedure con- 
sists of reacting the chromite at 550° to 650° C with an ex- 
cess of molten NaOH under oxidizing conditions to produce 
Ne^CKV The product from the fusion reaction is solidified, 
crushed, and leached with methanol in a countercurrent pro- 
cedure. The methanol leach removes the majority of the ex- 
cess NaOH while removing only a trace pf the Na2Cr0 4 . 
This separation can be accomplished because of the large 
difference in solubility of the two compounds in methanol. 
For example, the solubility of NazCr0 4 in a methanol solu- 



tion containing 10 pet NaOH is only 0.013 pet (4). The 
methanol solution is then evaporated to recover the NaOH, 
which is recycled to the fusion reactor. 

The residue from the methanol leach is water-leached to 
recover the remainder of the NaOH and the Na 2 Cr0 4 prod- 
uct. This solution is purified of Si and Al compounds by 
sparging with C0 2 to reduce the pH so that the Al and Si 
compounds precipitate. The carbonate ion formed during 
the C0 2 sparge is removed by adding lime to the solution to 
precipitate CaC0 3 . The final Na 2 Cr0 4 product is recovered 
from the aqueous solution by evaporative crystallization. 
The mother liquor exiting the crystallizer is evaporated, and 
the solids are recycled to the fusion reactor. The Na2Cr0 4 
product from this procedure is a basic chemical used in- 
dustrially and can be used to produce the other common Cr 
compounds in commerical use. 

The general equation for the fusion reaction of the 
chromite with the NaOH is 

FeO-Cr 2 3 + 4NaOH + 7/4 2 - 
2Na2Cr0 4 + l^FeA + 2H 2 



1 Chemical engineer. 

2 Group supervisor, Albany Research Center, Bureau of Mines, P.O. Box 
70, Albany, OR 97321. 





Abbreviations Used in This Paper 


°c 


degree Celsius 


cm 


centimeter 


e 


gram 


g/L 


gram per liter 


h 


hour 


mL 


milliliter 


mm 


millimeter 


min 


minute 


pet 


weight percent 


ppm 


part per million 



64 



Previous work by Chandra (5) showed that an excess of 
NaOH must be used to maintain a fluid reaction mixture. An 
NaOH-to-chromite weight ratio of ~ 4 (22.4 mole ratio) is 
typically necessary to maintain fluidity and to obtain good 
conversion of the Cr in the chromite to Na2Cr0 4 . Reaction 
products build up on the surface of the chromite particles, 
preventing further reaction, so the mixture must be kept 



well agitated to remove these surface products. Chandra 
used a small ball-mill-type reactor in his studies, but this 
type of reactor proved to be unworkable in larger sizes. A 
stirred-pot-type reactor was used in the present work. 
Studies are also being conducted in Japan on a similar pro- 
cedure using NaN0 3 as the oxidizing medium rather than 
air as used in the Bureau method (6-7). 




Makeup NaOH 

t 



concentrate / 
Air 



Solidified fusion 
product 



Solid-liquid 
separation 



Solid-liquid 
separation [ 




z 

J Oxidation and fusion 

I 550°-650° C 



Recycle methanol 



Methanol leach 



Condenser 



Solution 



Recycle 



_r-r ' — r. — I Kecyci' 

H Evaporation | Na £ H 



Water 



Water leach 



C0 2 sparge 



Recycle 
NaOH 



Condenser 



Solution 



1 



Water 
vapor 



-M Purification M Crystallization 



Residue to 
disposal 



Al and Si compounds Na 2 Cr0 4 product 
FIGURE 1.— Flowsheet for chemical processing of chromltes. 



65 



RAW MATERIALS 



The chromite concentrates tested in this study were ob- 
tained from a variety of sources in Alaska, California, Mon- 
tana, and Oregon. They were categorized in one of four 
groups: 

1. High-Cr (metallurgical-grade) chromite that con- 
tained a minimum of 46 pet Cr 2 3 with a Cr-Fe ratio 
>2.0:1. 

2. High-Fe (chemical-grade) chromite that contained 40 
to 46 pet Cr 2 3 with a Cr-Fe ratio of 1.5 to 2.0. 

3. Marginal chromite that met either the grade or Cr-Fe 
ratio requirements for one of the classifications above and 
very nearly met the other. 

4. Submarginal chromite that failed to meet the above 
classifications. 

These classifications were obtained from Dahlin (8). 
Four of the concentrates tested are listed in table 1 with 
their origin, composition, and classification of quality. The 
results of 10 additional samples are presented in Report of 
Investigations 8977 (9). 

Test results for two concentrates from Alaska are 
reported in this paper. One sample from Red Mountain was 
a high-Cr concentrate containing 56.4 pet Cr 2 3 with a Cr- 
Fe ratio of 2.8 {10). The Si impurity was 1.4 pet Si0 2 . The 
other sample from Alaska was from Red Bluff Bay (10). This 
was a high-Fe concentrate containing 41.7 pet Cr 2 3 with a 
Cr-Fe ratio of 2.0. The Si impurity was 8.0 pet Si0 2 . 



A concentrate from southern Oregon was derived from 
an Ni-Co laterite leach residue. This material was the 
residue remaining after processing in the Bureau's roast- 
leach procedure for recovering Ni and Co. Beneficiation of 
this residue resulted in a high-Fe chromite concentrate con- 
taining 41.5 pet Cr 2 3 with a Cr-Fe ratio of 1.8 (11). The 
Si0 2 content of this concentrate was 1.7 pet. 

A concentrate from the Mouat Mine in the Stillwater 
Complex in Montana was also tested. This was also a low- 
grade high-Fe material having a Cr-Fe ratio of 1.5 and a 
high Si content of 8.5 pet Si0 2 . 

The impurity content of the chromites is generally of 
two types: gangue components associated with the chromite 
grains, or lattice impurities in the chromite mineral itself. 
The Si impurity is generally in the form of silicate minerals 
such as olivine (Fe-Mg silicate) and serpentine (magnesium 
silicate). Silicon is not present in significant quantities in the 
form of silica minerals such as quartz. 

The chromite mineral is a spinel structure theoretically 
represented by the formula FeO*Cr 2 3 . Magnesium can 
substitute for the Fe 2 *, and Al 3 * and Fe 3 * can substitute for 
the Cr 3 * in the crystal lattice, giving the formula 
(Mg,Fe)0*(Al,Fe,Cr) 2 3 . In addition to the lattice im- 
purities, additional Fe in the form of magnetite (Fe 3 4 ) is 
also commonly associated with the chromite grains. 





TABLE 1.— Head analyses of chromite concentrates 






Location 


Sample 


Analysis, pet 


Cr-Fe 

ratio 


Quality 




Cr 2 3 


Fe 


MgO 


Al,0 3 


Si0 2 


classification 


Alaska: 

Kenai Peninsula . . . 

Baronof Island 
Southern Oregon 

Montana: 
Stillwater Complex. 


Red Mountain 

Red Bluff Bay 

Eight Dollar Mtn. 
laterite. 

Mouat 


56.4 
41.7 
41.5 

36.1 


13.7 
14.3 
16.1 

16.7 


15.2 

16.9 
12.4 

16.3 


8.8 

9.2 
22.3 

15.0 


1.4 
8.0 
1.7 

8.5 


2.8 
2.0 
1.8 

1.5 


High-Cr. 
High-Fe. 

Marginal. 



ALKALI FUSION 



EQUIPMENT AND EXPERIMENTAL PROCEDURES 

Most of the testing was conducted in a small, stainless 
steel, open-top reactor measuring 9 cm in diam by 15 cm 
deep. The reaction mixture was stirred with an attritioner- 
type mixer, and air was sparged into the mixture through 
two stainless steel tubes. The reactor was suspended in an 
electric furnace; to empty it, the reactor was removed from 
the furnace, and the contents were poured into a tray. 

A larger reactor was also constructed for use in prepar- 
ing larger samples for the countercurrent leaching studies 
and for comparing the Cr extractions obtained in the two 
different-sized reactors. The larger reactor measured 15 cm 
in diam by 31 cm deep. 

The metal extractions in the fusion reaction are defined 
as the amount of the various metals in the chromite con- 
verted to a water-soluble form. The reactor product was 
leached with water at 15 pet solids for 2 h to determine the 
soluble metal content. The resulting leach solutions were 
analyzed for Cr, Al, Si, Na, and NaOH. The residue from the 



leach step was analyzed for Cr. The Cr extraction was 
determined by a material balance between the Cr in the feed 
material, the Cr in the leach solution, and the Cr in the in- 
soluble residue remaining after water leaching. A material 
balance was not normally determined for the Al and Si. 
Their extractions were determined by comparing the 
amount of metal in solution with the amount in the chromite 
feed. The Cr extraction values represent the amount of Cr 
in the chromite converted to soluble Na 2 Cr0 4 and are not 
necessarily the overall maximum recovery that could be at- 
tained in a process. 

The variables studied in the fusion tests were reaction 
time, temperature, and NaOH-to-chromite ratio. The 
NaOH-to-chromite rato was based on the chromite content 
of the concentrate, not on its total weight. Such variables as 
stirring rate, particle size of the chromite, and airflow rate 
were not studied. The agitation rate and airflow were kept 
the same for all tests. Early testing showed that as long as 
the product was well stirred and sufficient airflow was 
maintained, these variables did not affect the results. The 



66 



concentrates were generally minus 65 mesh, although the 
laterite concentrate was minus 200 mesh. The particle size 
of the concentrates was the size necessary for liberation of 
the chromite mineral in the beneficiation studies. No addi- 
tional grinding or sizing of the chromite particles was per- 
formed. 

EXPERIMENTAL RESULTS AND DISCUSSION 

The Red Mountain concentrate is a high-grade, high-Cr 
material containing 1.4 pet Si0 2 . A limited amount of this 
concentrate was available, so extensive testing was not per- 
formed. However, all conditions tested with this material 
resulted in Cr extractions in excess of 90 pet (table 2). 
Relatively mild reaction conditions (2-h fusion time at 550° 
C with a NaOH-to-chromite ratio of 2) resulted in a Cr ex- 
traction of 94.9 pet. More severe conditions (4-h fusion time 
at 650° C with an NaOH-to-chromite ratio of 4) resulted in 
extractions as high as 98.8 pet. This material also stayed 
very fluid under all reaction conditions. 

The Red Bluff Bay chromite is a high-Fe chromite that 
contains 8.0 pet Si0 2 . The effect of time on the Cr extraction 
was not very significant with this chromite; the NaOH-to- 
chromite ratio was much more important (figs. 2-3, table 3). 
This material reacted quite rapidly with a Cr extraction of 
91.7 pet obtained after 1 h and a 94.4-pct extraction ob- 
tained after a 4-h reaction time at 650° C. Changing the 
NaOH-to-chromite ratio from 2 to 4 increased the Cr extrac- 
tion from 81.7 to 94.4 pet. This material also became less 
viscous as the NaOH content was increased. A ratio of 3 was 
the minimum practical amount with this concentrate, 
because at a ratio of 2 the reaction mixture was very viscous 
and would not pour out of the reactor. Data points are 
shown for a temperature of 550° C at NaOH-to-chromite 
ratios of 2 and 4 for comparison purposes, but no curve is 
drawn through the two points. 




KEY 
4-h reaction time — 
Cr Al Si 
650° C O A D 

550° C • A ■ 



2 3 

NaOH-CHROMITE.wt ratio 



FIGURE 2.— Effect of NaOH-chromlte weight ratio on metal 
extraction— Red Bluff Bay chromite. 



TABLE 2.— Results of chromite fusion tests, Red Mountain 
concentrate 



NAOH-chromite, 


Temp, 
°C 


Time, 
h 


Extraction, pet 


wt ratio 


Cr 


Al 


SI 


2:1 


550 
650 
550 
650 
550 
650 
550 
650 


2 

2 

4 
4 
2 
2 

4 
4 


94.9 
92.6 
95.5 
92.6 
94.8 
95.2 
98.0 
98.8 


81.8 
79.4 
81.3 
65.0 
80.6 
88.9 
75.7 
87.1 


53 8 


4:1 


50.8 
72.3 
27.7 
77 6 




71.4 
71.4 
65.3 



TABLE 3.— Results of chromite fusion tests, Red Bluff Bay 
concentrate 

(Small reactor unless otherwise indicated) 



NaOH-chromlte, 


Temp, 
°C 


Time, 
h 


Extraction, pet 


wt ratio 


Cr 


Al 


Si 


1:1 


650 
650 
550 
650 
550 
650 
650 
650 
650 
650 
650 


0.1 
2 
4 

4 
4 
4 
1 
2 
3 
4 
4 


7.9 

81.7 
79.8 
93.0 
88.6 
94.4 
91.7 
92.8 
95.0 
94.4 
96.9 


11.3 
43.5 
37.7 
60.7 
70.8 
65.9 
80.0 
77.9 
69.5 
65.9 
90.8 


11 8 


2:1 


20 9 


3:1 


26.8 
31 6 


4:1 


68 4 


4:1" 


55.0 
67.8 
56.4 
55.9 
55.0 
63 3 






'Large reactor. 














X 

Ld 



50 

40- 



30 



KEY 
4:l NoOH-chromite wt ratio 

Cr Al Si 
650° C O A D 

550 s C • A ■ 



REACTION Tl 



3 

/IE, 



FIGURE 3.— Effect of reaction time on metal extraction— Red 
Bluff Bay chromite. 



67 



The chromite concentrate obtained from the Eight 
Dollar Mountain laterite leach residue is a high-Fe chromite 
containing only 1.7 pet Si0 2 . The maximum Cr extraction 
obtained: from this material in the small reactor was 93.5 pet 
at 650° C, a reaction time of 4 h, and an NaOH-to-chromite 
ratio of 4. The NaOH-to-chromite ratio had very little effect 
on the Cr extraction (fig. 4, table 4), and the reaction mix- 
ture remained very fluid under all conditions tested. The ef- 
fects of time and temperature on Cr extraction were more 
pronounced, as shown in figure 5 and table 4. The Cr extrac- 
tion increased from 71.4 to 93.5 pet as the reaction time was 
increased from 1 h to 4 h at 650° C. At 550° C, the Cr ex- 
traction increased from 51.2 pet to 80.1 pet as the reaction 
time was increased from 1 h to 4 h. 

The Mouat concentrate from Montana was tested under 
a variety of conditions. Reaction times from 1 to 4 h were 
used at temperatures of 650° and 550° C, and the NaOH-to- 
chromite ratio was varied from 2 to 6. Ratios below 4 were 
totally unsuccessful because the mixture became too viscous 
to stir. As indicated in table 5 and figure 6, the best extrac- 
tions obtained with this material averaged 92.5 pet at an 
NaOH-to-chromite ratio of 4 and 91.7 pet at a ratio of 6. An 
NaOH-to-chromite ratio of 6 would be necessary in a large- 
scale operation, however, to obtain a product that will flow 



TABLE 4.— Results of chromite fusion tests, Eight Dollar 
Mountain laterite 




KEY 

4-h reaction time 

Cr Al Si 

650° C O A CD 

550° C • ▲ ■ 



2 3 4 5 

NaOH-CHROMITE,wt ratio 

FIGURE 4.— Effect of NaOH-chromite weight ratio on metal 
extraction— Eight Dollar Mountain laterite. 



(Small reactor unless otherwise indicated) 




NaOH-chromlte, 


Temp, 
°C 


Time, 
h 


Extraction, pet 


wt ratio 


Cr 


Al 


SI 


5:1 


650 
650 
650 
650 
650 
550 
550 
550 
550 
650 
650 
650 
650 
550 
550 
550 
550 
550 
650 


4 
4 
4 
4 
4 
4 
4 
4 
4 
4 
3 
2 
1 
4 
4 
3 
2 
1 
4 


92.6 
91.8 
93.5 
93.0 
89.4 
76.3 
80.0 
78.5 
80.1 
93.5 
88.9 
83.5 
71.4 
80.1 
78.5 
75.0 
62.2 
51.2 
94.7 


82.7 
84.5 
82.8 
80.5 
72.2 
70.8 
64.7 
58.8 
56.2 
82.8 
80.1 
73.9 
61.9 
56.2 
58.8 
53.9 
43.1 
38.1 
86.6 


69.7 


4:1 


73.4 
63.9 


3:1 


56.3 


2:1 


30.4 


4:1 


76.0 


3:1 


62.5 


2:1 


32.9 


4:1 


35.9 
63.9 


2:1 


69.0 
70.3 
69.6 
35.9 


4:1 ' 


32.9 
34.8 
40.5 
53.8 
73.9 



'Large reactor. 




20 

IO 





650° C, 4:l NaOH- O 

chromite wt ratio 

550° C, 2:l NaOH- • 
chromite wt ratio 



2 3 4 

REACTION TIME, h 

FIGURE 5.— Effect of reaction time on metal extraction- 
Eight Dollar Mountain laterite. 



68 



out of a reactor. The mixture prepared at a 4: 1 ratio is too 
viscous to pour, and even at the 6:1 ratio the mixture is fair- 
ly thick and does not flow readily. The data also indicate 
that a reaction time greater than 2 h does not greatly in- 
crease the Cr extraction at 650° C but has a greater effect 
at 550° C (fig. 7). A curve was not shown for the 550° C 
results because only two data points are available. The data 
are shown for comparison purposes. 

Chromium extractions in the large reactor were 
generally slightly higher than those obtained in the small 
reactor. This is shown in the results in tables 3-5. 

As mentioned earlier, limited testing was performed on 
10 other chromite concentrates with compositions ranging 
from high-Cr concentrates to submarginal concentrates. 
The poor-grade materials typically resulted in Cr extrac- 
tions in the 50- to 78-pct range, while the high-grade 
materials resulted in extractions in the 92- to 99-pct range. 

The viscosity of the fused reaction mixture ranged from 
almost waterlike to a pastelike consistency that would not 
flow out of the reactor. The lower grade chromites contain- 
ing high Fe or a combination of high Si + Al generally 
resulted in higher viscosity reaction products. Operating 
conditions resulting in very high viscosities also tended to 
result in somewhat lower Cr extractions. Moderate viscosity 
reaction products could still result in Cr extractions in the 
90-pct area, however. 



TABLE 5.— Results of chromite fusion tests, Mouat concentrate 



o 
< 

or 

r- 

X 

UJ 



100 
90 
80 
70 
60 
50 
40 
30 
20 




KEY 
4-h reaction time 
at 650" C 
O Cr 
A Al 
Q Si 




_L 



(Small reactor 


unless otherwise Indicated) 




NaOH-chromite, 


Temp, 


Time, 


Extraction, pet 


wt ratio 


°C 


h 


Cr 


Al 


SI 


6:1 


650 
650 


4 

4 


90.0 
92.4 


61.7 
67.8 


50.1 




72.9 




650 


4 


92.6 


69.9 


64.9 




550 


4 


77.9 


62.6 


83.0 




550 


4 


85.2 


64.8 


92.2 




650 


2 


88.9 


67.1 


81.0 




550 


2 


82.2 


55.1 


86.5 


5:1 


650 
550 


4 
4 


91.7 
81.3 


61.3 
49.2 


57.6 




71.2 


4:1 


650 


4 


90.5 


52.0 


45.2 




650 


4 


94.3 


61.5 


38.6 




650 


3 


88.0 


51.8 


53.3 




650 


2 


85.1 


50.8 


54.3 




650 


1 


80.9 


50.8 


54.8 




550 


4 


87.0 


48.1 


48.5 




550 


2 


63.3 


34.6 


73.8 


6:1' 


650 


4 


95.4 


70.6 


77.9 




650 


4 


94.3 


81.5 


80.5 



'Large reactor. 




I- 
O 
< 

H- 
X 

UJ 



80o^ 

70 

60 

50^ 

40 

30 

20 
IO 



-D- 
-A- 



KEY 

4:l NoOH-chromite wt ratio 
Cr Al Si 
650° C O A D 

550° C • A m 



I 3 5 7 

NaOH-CHROMITE, wt ratio 



I 2 3 

REACTION TIME, 




FIGURE 6.— Effect of NaOH-chromite weight ratio on metal 
extraction— Mouat chromite. 



FIGURE 7.— Effect of reaction time on metal extraction— 
Mouat chromite. 



69 



COUNTERCURRENT LEACHING 



EQUIPMENT AND PROCEDURE 

The solidified fusion product from the first step of the 
process was crushed and ground to minus 20 mesh. All 
grinding and screening operations were performed in a dry 
box to prevent the absorption of moisture by the material. 
Single-stage batch leach tests were conducted on this 
material to determine the appropriate conditions to use in 
countercurrent leach tests. These showed that the solids-to- 
liquid ratio and the amount of water in the methanol were 
important factors. In particular, the water in the methanol 
solvent had to be limited to 5 pet or less to prevent 
solubilization of Na 2 Cr0 4 . 

Countercurrent leach tests were performed in a step- 
wise manner using the Shanks system to simulate steady 
state conditions (12). Each leach stage was performed in a 
250-mL sample bottle using a small, three-bladed propellor 
for mixing. After leaching, the solid-liquid separation step 
was conducted by centrifuging the sample bottles. The liq- 
uid was decanted off and added to the next appropriate 
stage. The solids and the bottle were advanced to the next 
stage. In this manner, the solids remained in the same bottle 
for all three leach stages and did not have to be removed, 
minimizing handling losses. 

Fusion products from all four concentrates reported in 
the previous section were studied in countercurrent leach 
tests. These materials were leached in three countercurrent 
stages with methanol; then the residue from the methanol 
leach was leached with water in three countercurrent stages 
(fig. 8) in the equipment previously described. All the leach 
tests except one were conducted with 30 pet solids in the 
leach slurry. The other test was conducted at 15 pet solids. 
The 30-pct-solids value was chosen in order to produce 



methanol leach solutions that were nearly saturated with 
NaOH. This is necessary to minimize the energy required to 
evaporate the solution so the NaOH can be recycled. Leach 
time was 30 min in the methanol leach step and 10 min in the 
water leach. A particle size of minus 20 plus 32 mesh was 
used in most of the tests in the methanol step. The water 
leach step used the particle size resulting from the methanol 
leach, which was quite fine because the particles were 
broken down as the methanol removed the NaOH. A con- 
centration of 95 pet methanol and 5 pet water was used in all 
tests. 

RESULTS AND DISCUSSION 

The results indicate that methanol leaching removes 88 
to 94 pet of the unreacted NaOH. The higher extraction is 
obtained from fusion products containing a higher ratio of 
NaOH to chromite. As shown in table 6, only a trace of the 
Cr is found in the methanol solution. The aqueous solution 
contains the remainder of the NaOH and 90 to 99 pet of the 
soluble Cr. The remainder of the Cr and a trace of the NaOH 
are found in the residue from the water leach. These results 
are for three countercurrent stages. In the case of the 
Mouatconcentrate, where 10 pet of the soluble Cr remains 
in the leach residue, an additional stage would be necessary 
to remove this material. The NaOH concentration in the 
methanol solution ranged from 146 g/L for the Red Moun- 
tain fusion product to 224 g/L for the Mouat material. A 
saturated NaOH solution in methanol is approximately 240 
g/L NaOH. The Cr concentration in the aqueous solution 
was 80 to 90 g/L, and the NaOH was 35 to 80 g/L. A 
saturated solution at 25° C would contain approximately 
170 g/L Cr and 150 g/L NaOH. 



TABLE 6.— Results of two-step, three-stage countercurrent leach tests 





NaOH-chromlte, 
wt ratio 
In fusion 


Solids In 

leach, 

pet 


Methanol leach 


Water leach 


Residue 


Concentrate 


NaOH ext, 
pet 


Cr ext, 
pet 


NaOH ext, 
pet 


Cr ext, 
pet 


NaOH, 
pot 


Cr, 
pet 


Red Mountain 

Red Bluff Bay 

Eight Dollar 

Mountain 

Mouat 


2:1 

4:1 

4:1 
6:1 
6:1 


30 

30 

30 
30 
15 


88.8 
87.9 

84.0 
94.3 
92.7 


Tr 

Tr 

Tr 
Tr 
Tr 


11.1 
7.7 

15.6 
5.5 
7.2 


98.7 
96.5 

96.8 
90.0 
98.6 


0.1 
4.4 

.4 
.2 
.1 


1.2 
3.5 

3.2 

10.0 

.4 



ext Extraction. 



Tr Trace. 



NaOH-rich 
methanol- 

Fusion - 
product in 



m ^ 

2 3 

^ »-. 



Step I, methanol leach 



Methanol in 

Solids to 
step I 



Na 2 Cr0 4 -rich 
aqueous solution 

Solids from 
step I 



2 3 

to» to- 



Step 2, water leach 

FIGURE 8.— Two-step three-stage countercurrent leach. 



Water in 

Final residue 
to disposal 



70 



SOLUTION PURIFICATION 



No significant amount of impurities were found in the 
methanol solution. Aluminum and silicon were found in the 
10- to 50-ppm range. 

The major impurities that were solubilized in the 
aqueous solution by the fusion reaction were Si and Al. A 
minor amount of ferrous iron (Fe 2+ ) was also soluble but ox- 
idized on exposure to air and precipitated from solution. 
Magnesium was a major impurity in the chromite concen- 
trates but did not become soluble to any extent. Solution 
concentrations were typically 1 ppm Mg or less. As shown in 
tables 2-5 and figures 2-6, the Al extraction generally tend- 
ed to follow the same trend as the Cr extraction. This would 
be expected because the Al substitutes for Cr in the 
chromite lattice. As the Cr was reacted, the Al would also be 
exposed and react with the NaOH. 

The Si extraction appeared to be more random, 
although it generally decreased with time after increasing 
for the first hour of the reaction. Also, as shown in tables 2-5 
and figures 2-6, reaction at 550° C often resulted in greater 



extractions than at 650° C. These lower extractions may be 
due to the formation of higher-molecular-weight, insoluble 
sodium silicates as the reaction time and temperature in- 
crease. Increasing the NaOH-to-chromite ratio generally 
resulted in increased Si extraction. 

The total amount of Si found in the aqueous solution 
after countercurrent leaching ranged from 1.6 to 13 pet of 
the total Si content in the chromite. The Al content in the 
solutions ranged from 32 to 71 pet of the total amount in the 
chromite. These values are considerably lower than was ob- 
tained in single-stage leaching of the fusion product. The 
amount of Si extracted into the aqueous solution is par- 
ticularly reduced in the countercurrent leaching. 

The Si and Al compounds can be removed from solution 
by sparging with C0 2 . The pH of the solution was reduced 
from 12-13 to 9.5, and the compounds were precipitated. 
The carbonate ion formed during the C0 2 sparge is removed 
from the solution by the addition of lime. 



CRYSTALLIZATION 



Only preliminary crystallization work has been con- 
ducted. A batch crystallizer was constructed and operated 
for short periods with varying mother liquor compositions. 
The crystals that were formed were removed, washed, and 
analyzed for Na 2 Cr0 4 and NaOH. The corresponding 
mother liquor composition was also determined. The crystal 
size resulting from this procedure was very small, and the 
crystals were difficult to wash free of the mother liquor. 
Testing was conducted at 65° and 90° C. Preliminary 



results from these tests indicated that Na 2 Cr0 4 crystals 
containing less than 0.1 pet NaOH can be produced from 
mother liquors containing an NaOH-to-chromate ratio of as 
high as 10. Concentration of NaOH was aproximately 57 pet 
(860 g/L). A semicontinuous crystallizer has been con- 
structed and is presently being operated. Crystals with a 
much larger size, minus 16 plus 32 mesh, have been pro- 
duced with this equipment and again show NaOH contents 
of less than 0.1 pet. 



SUMMARY AND CONCLUSIONS 



Laboratory-scale testing showed that low-grade 
domestic chromites that are not sutiable for chemical proc- 
essing by present commercial methods can be treated suc- 
cessfully by a procedure devised by the Bureau of Mines. 
The procedure involved reacting the chromites with fused 
NaOH under oxidizing conditions to form Na 2 Cr0 4 . The 



Na 2 Cr0 4 was then recovered by leaching and crystallization. 
Chromium extractions as high as 98.9 pet were obtained in 
the fusion step from high-Cr concentrates. Marginal high- 
Fe concentrates resulted in Cr extractions in the 90- to 
94-pct range. 



REFERENCES 



1. Papp, J. F. Chromium. Ch. in Mineral Facts and Problems, 
1985 Edition. BuMines B 675, 1985, pp. 139-156. 

2. Copson, R. L. Production of Chromium Chemicals. Ch. in 
Chromium, Volume 1, Chemistry of Chromium and Its Compounds, 
ed. by M. J. Udy. Reinhold, 1956, pp. 262-282. 

3. Hartford, W. H., and R. L. Copson. Chromium Compounds. 
Ch. in Kirk-Othmer Encyclopedia of Chemical Technology, ed. by 
A. Standen. Wiley, v. 5, 2d ed., 1964, pp. 473-516. 

4. Kashiwase, K., G. Sato, E. Narita, and T. Okabe. Solubility of 
Sodium Chromate in Sodium Hydroxide Solution and in Methanol 
Solution. Nippon Kagaku Kaishi, v. 7, 1974, pp. 1224-1229. 

5. Chandra, D., C. B. Magee, and L. Leffler. Extraction of 
Chromium From Low-Grade Chromium-Bearing Ores (contract 
GO284009, Denver Res. Inst.). BuMines OFR 151-82, 1982, 161 
pp.; NTIS PB 83-106781. 

6. Okabe, T., and K. Kashiwase. Process for Production of Alkali 
Metal Chromates. U.S. Pat 3,859,412, Jan. 7, 1975. 



. 7. Kashiwase, K, M. Mita, T. Kon, and T. Okabe. Methanol 
Leaching of Reaction Product of Chromite With Molten Sodium 
Salts. Nippon Kagaku Kaishi, v. 9, 1975, pp. 1491-1495. 

8. DaWin, D. C, L. L. Brown, and J. J. Kinney. Podiform 
Chromite Occurrences in the Caribou Mountain and Lower Kanuti 
River Areas, Central Alaska (In Two Parts). BuMines IC 8916, 
1983, 15 pp. 

9. Hundley, G. L., D. N. Nilsen, and R. E. Siemens. Extraction of 
Chromium From Domestic Chromites by Alkali Fusion. BuMines 
RI 8977, 1985, 14 pp. 

10. Dahlin, D. C, D. E. Kirby, and L. L. Brown. Chromite 
Deposits Along the Border Ranges Fault, Southern Alsaka (In Two 
Parts). BuMines IC 8991, 1985, 37 pp. 

11. Kirby, D. E., D. R. George, and C. B. Daellenbach. Chromium 
Recovery From Nickel-Cobalt Laterite and Laterite Leach 
Residue. BuMines RI 8676, 1982, 22 pp. 

12. Treybal, R. E. Mass-Transfer Operations. McGraw-Hill, 1955, 
pp. 590-591. 



BuMines IC 9087: Chromium-Chromite: Bureau of Mines Assessment and Research 



71 



PYROMETALLURGICAL PROCESSING OF DOMESTIC CHROMIUM 

RESOURCES 

By R. H. Nafziger 1 



ABSTRACT 



This paper reviews pyrometallurgical research con- 
ducted by the Bureau of Mines to prepare ferrochromium 
and other products. Emphasis is placed on the problems en- 
countered in using domestic chromite sources. Advantages 
and disadvantages of each process are addressed. 

The Bureau demonstrated that a wide variety of 
domestic Cr resources can be used to prepare suitable ferro- 
chromium by electric arc smelting. At first, open-bath condi- 
tions were used; later, submerged-arc operations proved 
more feasible and required less energy. 



More recently, basic research by the Bureau delineated 
the conditions under which domestic Cr concentrates can be 
prereduced in the solid state prior to melting. Domestic 
materials were prereduced satisfactorily in a batch rotary 
kiln and melted to produce ferrochromium. The results also 
delineated the advantages and disadvantages of prereduc- 
tion and melting compared with direct-smelting techniques. 
Successful scrap recycling techniques also were demon- 
strated. 



INTRODUCTION 



Over 75 pet of domestic Cr consumption was used in the 
metal industry in 1981 (1). Increased hardness, increased 
creep and impact strengths, and increased resistance to cor- 
rosion or oxidation are among the attributes that make Cr 
an essential additive to iron, steel, and nonferrous alloys. 
Chromium is typically added as ferrochromium to these 
metals. This product must be produced from chromites us- 
ing some form of pyrometallurgical processing. Ferro- 
chromium accounts for nearly 55 pet of total domestic Cr 
consumption (2). 

Traditionally, pyrometallurgical techniques are used to 
convert Cr ores or concentrates to ferrochromium. Fluxes 
and reductants are added to these ores or concentrates, and 
the mixture is smelted in a three-phase ac electric arc fur- 
nace. Chromium metal also can be produced by pyro- 
metallurgical processing. A typical process involves the 
reduction of pure chromia (Cr 2 3 ) by finely divided Al metal. 

Conventional electric arc furnace techniques have been 
used to smelt Cr concentrates to produce ferrochromium for 
many years. Ideally, the charge should be lumpy to minimize 
both the loss of Cr contained in fines and segregation with 
resultant nonreduction during smelting. Unfortunately, 
supplies of hard, lumpy ore are decreasing and are becom- 
ing more costly. Pelletizing or briquetting the feed is an 
alternative, but these processes require fine grinding, addi- 
tion of binders for agglomeration, and sintering, all of which 
are labor and energy intensive. Relatively high electrode 
consumption and slag burden contribute to the disadvan- 
tages of conventional smelting processes. 

Prereduction of Cr ores and concentrates prior to 
melting promises some advantages over direct smelting. 
Among these are (1) more readily available carbonaceous 
reductants can be used for partial reduction so that elec- 
trical energy is not required to reduce the entire charge, (2) 
less C is required during melting, resulting in easier opera- 
tional control with fewer impurities introduced into the 
system, (3) increased productivity can be realized, (4) higher 



quality slags could be prepared, (5) more 2 and volatiles are 
removed prior to smelting, (6) lower electrode consumption 
can be obtained, (7) higher recoveries can be realized, (8) 
smoother melting operation is possible, and (9) the heat 
generated in the prereduction process can be used. 

More recently, plasma processing of Cr resources has 
attracted considerable attention owing to numerous stated 
advantages (3). Although it has conducted no experimental 
work in this field, the Bureau of Mines is monitoring 
developments closely. 

For many decades, the Bureau of Mines was engaged in 
research directed toward the more efficient pyrometal- 
lurgical processing and recycling of Cr resources and 
toward a decrease in U.S. dependence on imports. Roasting 
studies to more efficiently use domestic deposits began in 
Bureau laboratories nearly 60 years ago. Smelting research 
on the Montana Cr concentrates in the Stillwater Complex 
started in 1936, and work on many Cr materials continued 
through 1982. Prereduction and melting studies were con- 
ducted intermittently from 1963 through 1980. 

The objective of this paper is to review Bureau research 
in the pyrometallurgical processing and recycling of Cr 
resources, including roasting, smelting, and prereduction 
and melting, with emphasis on domestic deposits. 



1 Research supervisor, Albany Research Center, Bureau of Mines, P.O. 
Box 70, Albany, OR 97321. 



Abbreviations Used in This Paper 


°C 
h 


degree Celsius 
hour 


kg 

kg/h 

kg/min 

kg/mt 

kW 


kilogram 

kilogram per hour 
kilogram per minute 
kilogram per metric ton 
kilowatt 


kW-h/mt 


kilowatt hour per metric ton 


mm 


minute 


mt 


metric ton 


pet 


weight percent 



72 



SMELTING 



OPEN-BATH TESTS 

The Bureau has conducted extensive smelting studies 
on unreduced lower grade Cr concentrates over the past 
several decades. Most of the earlier research that was begun 
in 1948 was conducted using open-bath (or open-arc) condi- 
tions wherein the molten bath is not covered either with an 
unmelted charge or with a reductant such as woodchips. 
Under these conditions, excessive heat losses, electrode con- 
sumption, and refractory wear can be expected. 

Stillwater Concentrates 

A majority of the open-bath experiments were ac- 
complished on concentrates from the Mouat Mine in the 
Stillwater Complex in Montana. Wessel and Rasmussen 
(4-5) smelted Mouat material in a basic magnesite-lined, 
single-phase, 227-kg-capacity electric arc furnace using a 
subbituminous coal or a char made from this coal. A C-Cr 
ratio of 1.02 in the charge yielded a ferrochromium with a 
typical Cr-Fe ratio of 1.36. Chromium and iron recoveries in 
the metal were usually 97 and 94 pet, respectively. Silicon 
and carbon contents were inversely related and ranged from 
0.2 to 5 pet and from 4 to 7 pet, respectively. Decreases in 
the C-Cr ratio in the charge from 1.02 to 0.41 resulted in 
lower Cr and Fe recoveries in the metal (down to 16 pet and 
as low as 55 pet, respectively) and hence poorer metal. Tests 
in an acid-lined furnace produced metal having a higher Si 
content (from 7 to 14 pet) and Cr-Fe ratio (up to 1.53) than 
tests in a furnace with a basic lining. Recoveries for Cr and 
Fe were 84 to 95 pet and 76 to 90 pet, respectively. One test 
in a three-phase furnace using a magnesite lining resulted in 
a ferrochromium with an average Cr-Fe ratio of 1.46 and 
demonstrated the feasibility of this technique for producing 
a satisfactory product. 

Hunter (6) conducted smelting tests in a 23-kg-capacity, 
single-phase electric arc furnace on the high-Fe Cr concen- 
trates characteristic of the Stillwater materials to selective- 
ly reduce the iron, thereby increasing the Cr-Fe ratio. Car- 
bon additions in the form of coke to the charges ranged from 
40 to 100 pet of the stoichiometric requirements, and acid to 
neutral slags were used. The Fe was readily separated from 
the Cr, and 89-pct-Cr recovery was realized in the slag. The 
slag subsequently was reduced to produce a satisfactory fer- 
rochromium. 

More recent research involved open-bath smelting of 
selected Stillwater concentrates in a single-phase, 100-kg- 
capacity electric arc furnace to provide baseline data for 
comparison with prereduction and melting tests (7-8). Open- 
bath tests required at least a neutral slag to achieve Cr-Fe 
levels of 1.5 and Cr recoveries of only 60 pet in the fer- 
rochromium. A more basic slag was deemed preferable for 
better Cr recoveries and higher Cr-Fe ratios. 

Northern California Ore 

A chromium ore having a Cr-Fe ratio of nearly 3 occurs 
in northern California in widely disseminated podiform 
deposits. Some of this material was smelted under open- 
bath conditions with coal char (115 pet of the stoichiometric 
requirement) in a single-phase, 100-kg-capacity electric arc 



furnace (7-8). A satisfactory ASTM grade C ferrochromium 2 
was produced with a slightly acid slag. 



South-Central California Concentrates 

A metallurgical-grade Cr concentrate from south- 
central California having a Cr-Fe ratio of 1.9 was smelted in 
the same furnace under open-bath conditions (7-8). A 
satisfactory ASTM grade A ferrochromium was produced 
using a basic slag. 

This material also was used to prepare a very-high-C fer- 
rochromium for use in a fusion-welding process for hard- 
facing. Open-bath conditions were used to prepare the 
material both in a 100-kg, single-phase, ac electric arc fur- 
nace and in a 1-mt, three-phase ac furnace (9). Approximate- 
ly 110 pet of the stoichiometric C requirement was used with 
a basic slag. The resulting ferrochromium contained 59 to 
64 pet Cr and 25 to 31 pet Fe. Carbon levels in the metal 
from all tests were greater than 9 pet. Hard facings applied 
by a fusion-welding process using the produced fer- 
rochromium demonstrated acceptable properties in subse- 
quent tests. Smelting to produce a high-C ferrochromium 
required a basic slag with an Al 2 3 -MgO ratio of 1. 



SUBMERGED-ARC TESTS 

In addition to open-bath tests, the Bureau devised 
techniques for smelting a wide variety of unreduced Cr 
materials using submerged-arc conditions. Typically, these 
techniques involved establishing a small molten pool and 
then maintaining the furnace full of unmelted charge 
materials during smelting. A majority of the reductant was 
present as uniform woodchips or hogged fuel (waste wood 
products such as edgings, trimmings, and splinters proc- 
essed through a machine known as a hog). The arcs were 
submerged beneath the unmelted material throughout the 
test. The "dry-top" cover conserved heat, minimized the 
need for agglomeration, and decreased refractory erosion 
and electrode consumption. 



Stillwater Concentrates 

In 1952, the Bureau resumed smelting research on 
domestic Cr materials. Early results demonstrated that 
finely divided concentrates could be smelted directly in a 
dry-top operation without agglomeration or mixing with 
lumpy ores when hogged fuel was used (5). This lower densi- 
ty charge material facilitated metal-slag separation without 
the use of high temperatures. Further experiments showed 
that useful ferroalloys could be produced from high-Fe 
chromites typical of those found in the Stillwater Complex 
(10). 

These tests failed to improve the Cr-Fe ratio, but high-C 
ferrochromium was produced under acid smelting condi- 
tions. From 132 to 141 pet of the stoichiometric C require- 
ment, approximately 100 kg of concentrate, and an acid slag 



2 For high-C ferrochromium, ASTM grade A has, in weight percent, 52-58 
Cr, 6-8 C, 6 max Si, 0.040 max S, and 0.030 max P. Grade B has 55-64 Cr, 4-6 
C, 8-14 Si, 0.040 max S, and 0.030 max P. Grade C has 62-72 Cr, 4-9.5 C, 3.0 
max Si, 0.060 max S, and 0.030 max P. 



73 



appeared optimum. Other alloys such as ferrochromium- 
silicon, low-C ferrochromium, and Cr-Mn-Si were suc- 
cessfully produced and tested (10). 

Stockpile concentrates from the Stillwater Complex 
were nodularized in later tests in a rotary kiln with fluxing 
constituents (quartz, limestone, and fluorspar) and smelted 
using coal and/or coal char. In addition, high-C fer- 
rochromium was successfully prepared from these stockpile 
concentrates using hogged fuel as the major reductant. 
Chromium and iron recoveries ranged from 87 to 93 pet. 
Silicon levels in the ferrochromium were inversely propor- 
tional to slag basicity and C content (11). 

More recent tests using woodchips to provide approx- 
imately 75 pet of the desired C requirements (7-8). Six dif- 
ferent reductants (charcoal, coke breeze, coal char, coal, 
metallurgical coke, and petroleum coke) were evaluated. 
Coal char was the most reactive of these and provided the 
highest Cr recovery, lowest energy consumption, and 
highest metal weight. An ASTM grade A, high-C fer- 
rochromium 3 was produced when 110 to 120 pet of the 
stoichiometric C requirement was used, with 60 pet of the C 
present as woodchips and an initial slag basicity of 1.1 



Central Oregon Chromium Ore 

Early Bureau research included a few tests on a refrac- 
tory ore from Grant County, OR (12-13). Energy consump- 
tion was comparable to that when Cr concentrates were 
smelted, and Cr recovery was only 5 pet lower than that ob- 
tained when smelting the concentrates (approximately 93 
pet). Low-C ferrochromium-silicon was judged to be an 
especially desirable product to make from these central 
Oregon ores. 



Oregon Beach Sands 

Concentrates from the southern Oregon coast with 
similar Cr-Fe ratios of 1.4 also were smelted by the Bureau 
(10). Results were similar to those obtained with Stillwater 
materials described previously (10). 



Northern California Chromium Ore 

Different ores from northern California having Cr-Fe 
ratios ranging from 1.3 to 1.5 could not be smelted to pro- 
duce satisfactory commercial alloys using submerged-arc 
techniques owing to high energy requirements (2,000 
kW-h/mt Cr produced) and low Cr recoveries (78.5 pet). 
Coke and hogged fuel were used as reductants (14). 
However, beneficiation prior to smelting increased the pro- 
duction rate 1.8 times, the electrical energy consumption 
decreased 39 pet, less flux was required to yield a fluid slag, 
and the Cr content of the alloy increased nearly 30 pet (to 59 
pet) (U). 

Additional smelting tests on mixtures of lump ore and 
concentrates from northern California and southern Oregon 



demonstrated that submerged-arc conditions could produce 
a satisfactory high-C ferrochromium containing 60 pet Cr, 
with a Cr recovery of 93 pet in the metal (15). Energy con- 
sumption was relatively low (4,365 kW-h/mt alloy). 

More recent submerged-arc smelting experiments on a 
northern California metallurgical-grade ore using 115 pet of 
the stoichiometric C requirements showed that a more acid 
slag yielded more metal and Cr recovery was higher (up to 
96 pet). Both ASTM grades B and C high-C ferrochromium 4 
were prepared from this ore (7-8). 



South-Central California Chromium 
Concentrate 

A metallurgical-grade Cr concentrate from south- 
central California was smelted using the aforementioned six 
reductants and from 100 to 110 pet of the stoichiometric C 
requirements. Coal char provided the most satisfactory 
overall submerged-arc smelting operation, followed by char- 
coal and metallurgical coke. An ASTM grade C high-C 
ferrochromium 5 was produced when coal char was used 
(7-8). In this case, a more basic slag was desirable. 



Laterites 

The most recent Bureau Cr smelting research involved 
the use of a concentrate derived from residues generated by 
the processing of Ni and Co from domestic laterites. (16). 
These concentrates contained approximately the same 
amount of Cr and less Fe than other offgrade Cr concen- 
trates smelted previously (6-8, 11). With respect to fluxing 
constituents, A1 2 3 was higher, but MgO and Si0 2 levels 
were comparable. Results of submerged-arc smelting tests 
showed that metallurgical-grade coke provided the best 
quality ferrochromium when 120 pet of the stoichiometric C 
requirement was used. A high-C ferrochromium was 
smelted satisfactorily from the concentrate in a 100-kg- 
capacity furnace, provided that suitable flux additions were 
made and that the P and S contents can be decreased during 
the steelmaking process. Agglomeration of the charge 
materials was not required. 



COMPARISON OF OPEN-BATH AND 
SUBMERGED-ARC SMELTING 

In general, submerged-arc smelting of Cr ores and con- 
centrates is preferred over open-bath smelting. However, 
the latter technique often results in higher Cr contents in 
the metal. Results throughout the years of Bureau research 
support this conclusion. Noteworthy are the higher produc- 
tivity and lower apparent electrical energy and electrode 
consumption for submerged-arc smelting. In submerged-arc 
operations, furnace operation was smoother and refractory 
wear was less, particularly at the slag level. Examples are 
given in table 1 (7-8). 



1 See footnote 2. 



'• 5 See footnote 2. 



74 



TABLE 1. 


—Comparison of open-bath and submerged-arc smelting tests on various domestic chromltes 








Stillwater 
concentrate 


Northern 
California ore 


South-central 
California concentrate 




Submerged 
arc 


Open 
bath 


Submerged 
arc 


Open 
bath 


Submerged 
arc 


Open 
bath 


Metal: 

Cr 

Cr-Fe ratio 

Cr recovery 

Slag: 

Cr 

Fe 

Metal In cone 


pet . . 

pet . . 

pet . . 

pet . . 

.... kg/mt . . 


44 
1.17 

97 

.35 
1.53 
609 
1.16 


48 

1.15 

60 

9.01 
1.98 
331 
3.66 


60 

2.60 

96 

3.87 
2.07 
503 
1.91 


66 

2.75 

77 

6.83 
4.17 
430 
1.64 


63 

2.59 

95 

1.57 
1.77 
464 
2.42 




56 

1.86 

45 

11.4 
3.49 
226 
5.25 







PREREDUCTION AND MELTING 



BASIC RESEARCH 

The Bureau has engaged in considerable basic research 
to ascertain the mechanism of solid-state chromite re- 
duction, as well as the effects of variables such as 
temperature, composition, and reductant on chromite 
reduction. Hunter (1 7) reduced Stillwater Complex Cr con- 
centrate with graphite in Ar at 1,030° to 1,630° C. Signifi- 
cant reduction occurred above 1,100° C. Results indicated 
that the reduction of Fe and Cr oxides occurred concurrent- 
ly. The temperature of reduction significantly affected the 
reduction behavior, as shown in table 2 (17). 

Nafziger (18) studied the reduction of a Cr concentrate 
from the Stillwater Complex and an ore from northern 
California using four reductants (coke breeze, coal char, 
metallurgical coke, petroleum coke) to determine optimum 
reductants and other variables such as temperature and 



reduction time for the solid-state prereduction of chromites 
prior to melting. With respect to the degree of reduction 
and metallization, coal char generally was the preferred 
reductant in laboratory experiments in Ar between 1,100° 
and 1,500° C. The degree of reduction or metallization was 
proportional to the time and/or temperature used. The rate 
of reduction was greatest during the first 15 min. The Still- 
water concentrate was more easily reduced than the nor- 
thern California ore, especially at the higher temperatures. 
Simple kinetic equations could not adequately describe the 
reduction mechanisms for both Cr materials. The reduction 
may be nucleation controlled, especially under conditions of 
interest in commercial operations, where total metalliza- 
tions as high as possible (80 to 90 pet) are desired. 



PREREDUCTION EXPERIMENTS 



TABLE 2.— Carbothermlc reduction 
of Mount chromium concentrate 



Temp, 
°C 

1,033 


Reduction 
pet 

1.6 


1,192 


18.2 


1,205 


15.7 


1,283 


30.0 


1,367 


63.1 


1.517 


89.2 



The aforementioned fundamental data were used by the 
Bureau as a basis for preparing four prereduced Cr 
materials in a gas-fired, 500-kg batch rotary kiln prior to 
melting (7-8). The Cr materials were pelletized with coal 
char, dried, and charged with more readily available coke 
breeze into the kiln. Reduction was accomplished between 
1,100° and 1,375° C. The prereduced pellets were dis- 
charged into an Ar-filled hopper and covered with coal char 
to prevent reoxidation. Results are tabulated in table 3. 



TABLE 3.— Results of prereduclng four domestic chromium materials 





Stillwater 

chromium 

concentrates 


Northern 

California 

ore 


South-central 

California 

concentrate 




Mouat 


Benbow 




Total (Fe + Cr) metallization pet . . 

Temperature, °C: 

Start of reduction 

End of reduction 

Reduction complete h . . 

Product, pet: 

Cr 

Fe 


60 

1,150 

1,350 

3 

26 
17 


67 

1,150 

1,325 

2 

26 
16 


78 

1,150 

> 1,400 

3 

32 
12 


62 

1,150 

ND 

3 

32 
12 



75 



MELTING TESTS ON PREREDUCED 
MATERIALS 

Prereduced Cr materials from the four aforementioned 
sources were melted in a 100-kg-capacity, single-phase ac 
electric arc furnace, and the results were compared with 
those obtained on unreduced materials. The prereduced Cr 
materials were mixed with fluxing constituents and coal 
char and/or other reductants (where necessary) and melted. 
For the materials from the Stillwater Complex and from 
south-central California, slag basicities of 1.1 and 110 pet of 
the stoichiometric C requirements were used. Melting tests 
for the northern California ore used a slag basicity of 1.2 
and 150 pet of the stoichiometric C requirement (7-8). 
Results are shown in table 4. 



COMPARISONS BETWEEN PREREDUCTION— 
MELTING AND DIRECT SMELTING 

Metal quality, as reflected in the compositions, was 
similar in material derived from direct smelting and from 
melting of prereduced feed. Metal melted from prereduced 
material generally possessed greater S levels owing to 
relatively high levels in the reductants used for prereduc- 
tion. Phosphorus contents also were higher. With the excep- 



tion of the Cr concentrate from south-central California, 
prereduction yielded more C and generally less Si in the 
metal after melting (7-8). 

As shown in table 4, prereduction generally resulted in 
higher productivity and lower electrical energy consump- 
tion, with the exception of the Mouat material, which 
showed no significant advantages in prereduction other 
than metal Cr content (7-8). 



ADVANTAGES AND DISADVANTAGES OF 
PREREDUCTION 

The research conducted by the Bureau on Cr materials 
indicates that many of the advantages of prereduction 
enumerated earlier in this paper could be realized. 
However, it was not proven that higher quality slags were 
more easily attainable or that lower electrode consumption 
was obtainable. One disadvantage of prereduction may be 
increased metal S, which would require refining during or 
after the melting operation. Total energy consumption may 
not be improved significantly as a result of prereduction. 
Other disadvantages include the necessity for fine grinding 
and close temperature control to prevent excessive sinter- 
ing during prereduction. 



TABLE 4.— Results of prereduction and melting of four domestic 
chromium materials compared with smelting unreduced materials 





Stillwater chromium 
concentrates 


Northern 

California 

ore 


South-central 

California 

concentrate 




Mouat 


Ben bow 




Unre- 
duced 


Prere- 
duced' 


Unre- 
duced 


Prere- 
duced' 


Unre- 
duced 


Prere- 
duced 2 


Unre- 
duced 


Prere- 
duced 3 


Melt rate kg/min . . 

Electrical energy consump- 
tion kW«h/mt metal. . 

Electrode consumption . . . kg/mt metal . . 

Metal: 

Cr-Fe ratio 

Cr pet.. 

Cr recovery pet . . 

Slag, pet: 

Cr 

Fe 

Slag-metal wt ratio 

Productivity kg/h metal . . 


1.0 

4,540 
58.0 

1.17 

44.3 

99 

0.35 
1.53 
1.16 
16.0 


0.8 

4,410 
58.7 

1.59 

53.3 

82 

4.41 
3.04 
1.79 
16.2 


0.9 

6,230 
50.8 

1.73 

52.8 

93 

0.72 
0.57 
2.61 
11.0 


0.8 

4,940 
50.4 

1.55 

52.9 

77 

0.52 
1.02 
2.02 
14.8 


1.0 

6,420 
54.4 

2.64 

57.6 

83 

2.06 
0.95 
1.91 
11.1 


1.3 

3,400 
44.8 

2.21 

56.7 

62 

0.31 
2.80 
1.94 
19.2 


0.9 

5,920 
53.9 

2.59 

60.3 

76 

1.57 

1.77 

2.42 

9.6 


0.9 

3,975 
51.4 

2.54 

63.1 

71 

1.58 
2.07 
2.44 
13.9 



' Average of 3 tests. 2 Average of 2 tests. J Average of 4 tests. 



SCRAP PROCESSING 



It has long been recognized that a significant domestic 
resource for Cr is alloy scrap. Accordingly, the Bureau con- 
tracted with several outside organizations to devise a proc- 
ess for recovering Cr from superalloy scrap. A 
pyrometallurgical oxidation-reduction approach was chosen 
(19). Superalloy scrap was melted in 20- and 50-kW induc- 
tion furnaces. Oxidizing gases were introduced to separate 
the Cr into a slag phase. Chromium removal exceeding 99 
pet could be achieved. In this step, a metal fraction rich in Ni 
and Co was obtained. The Cr-bearing slag was reduced with 
FeSi (75 pet Si) to produce a suitable ferrochromium (con- 



taining 65 pet Cr) with a Cr yield over 85 pet with up to 95 
pet recovery. Aluminum and carbon also could be used as 
reducing agents (19). An alternative process involves 
melting and partly oxidizing a blended scrap charge, follow- 
ed by careful sulfidation to form a partial matte (17 to 25 pet 
S) of Ni 3 S 2 , Cr 2 S 3 , and an Ni-rich metal phase. Mineral pro- 
cessing techniques were used to separate metals and 
sulfides. The Cr 2 S 3 containing some Ni can be roasted in a 
fluidized bed to decrease S to 0.02 pet and aluminothermi- 
cally reduced to produce a metal with 0.033 pet S (20). Satis- 
factory Cr recoveries (85 pet) were realized. 






76 



CONCLUSIONS 



Extensive pyrometallurigcal experiments by the Bureau 
of Mines have shown that it is possible to prepare satisfac- 
tory ferrochromium from a wide variety of lower grade 
domestic Cr materials. For smelting unreduced materials, 
submerged-arc techniques generally provide better results 
than open-bath methods, with respect to both furnace 
operations and product quality. Byproduct hogged fuel or 
woodchips can be used effectively as reductants. 

Prereduction and melting offer an alternative process- 
ing technique for Cr materials. However, advantages of this 
method over direct smelting have not been clearly estab- 
lished. A pyrometallurgical oxidation-reduction technique 



also was used successfully to recover Cr from superalloy 
scrap. 

It is evident from this review that more research is re- 
quired to evaluate the efficiencies of present processes and 
to propose new processes (21). A better understanding of 
physical properties and reaction mechanisms applicable to 
reduction and smelting is needed. Thermochemical and 
kinetic investigations are required, as is a more thorough 
knowledge of relevant crystal structures to increase the ef- 
fectiveness of the pyrometallurgical processing of Cr. 
Emerging technologies such as prereduction and plasma arc 
melting for Cr should be evaluated further. 



REFERENCES 



1. Kirby, R. C, and J. F. Papp. Perspective on Chromium From 
the U.S. Bureau of Mines. Chromium Rev., v. 1, No. 1, 1983, pp. 
6-7. 

2. Papp, J. F. Chromium. Ch. in BuMines Minerals Yearbook 
1983, v. 1, pp. 203-220. 

3. Dwyer, J. J. The Promise of Plasma. 33 Metal Producing, v. 22, 
No. 2, 1984, pp. 37-41. 

4. Wessel, F. W., and R. T. C. Rasmussen. Ferrochromium From 
Low Grade Chromite Ores and Concentrate. J. Met., v. 2, No. 8, 
1950, pp. 984-988. 

5. Rasmussen, R. T. C. Electric Smelting at Bureau of Mines 
Seeks Utilization of Northwest Ores. J. Met., v. 4, No. 12, 1952, pp. 
1273-1279. 

6. Hunter, W. L., and L. H. Banning. Pyrometallurgical 
Beneficiation of Offgrade Chromite and Production of Fer- 
rochromium. BuMines RI 6010, 1962, 16 pp. 

7. Nafziger, R. H., P. E. Sanker, J. E. Tress, and R. A. McCune. 
Prereduction and Melting of Domestic Chromites. Proc. Electr. 
Furn. Conf., v. 38, 1981, pp. 27-45. 

8 Prereduction and Smelting of Domestic (U.S.) Chromites 

From Montana and California. Ironmaking and Steelmaking, v. 9, 
No. 6, 1982, pp. 267-277. 

9. Sanker, P. E., R. H. Nafziger, and G. H. Reynolds. Preparation 
of Specialty Ferrochromium (9 wt% C) From a Domestic Chromite. 
J. Met., v. 32, No. 3, 1980, pp. 49-52. 

10. Walsted, J. P. Electric Smelting of Low-Grade Chromite Con- 
centrates. BuMines RI 5268, 1956, 28 pp. 

11. Hunter, W. L., and L. H. Banning. Electric Smelting of Mon- 
tana Chromite Concentrates. BuMines RI 5775, 1961, 30 pp. 



12. Banning, L. H. The Role of the Electric Arc Furnace in Utiliz- 
ing Some Strategic Off-Grade Ores. J. Electrochem. Soc, v. 101, 
No. 12, 1954, pp. 613-621. 

13. Hundhausen, R. J., L. H. Banning, H. M. Harris, and H. J. 
Kelly. Exploration and Utilization Studies, John Day Chromites, 
Oregon. BuMines RI 5238, 1956, 31 pp. 

14. Hunter, W. L., and G. V. Sullivan. Utilization Studies on 
Chromite From Seiad Creek, Calif. BuMines RI 5576, 1960, 37 pp. 

15. Hunter, W. L., and G. A. Kingston. Ferrochromium From 
Western Metallurgical-Grade Chromite. BuMines RI 5897, 1961, 9 
pp. 

16. Kirby, D. E., D. R. George, and C. B. Daellenbach. Chromium 
Recovery From Nickel-Cobalt Laterite and Laterite Leach 
Residue. BuMines RI 8676, 1982, 22 pp. 

17. Hunter, W. L., and D. L. Paulson. Carbon Reduction of 
Chromite. BuMines RI 6755, 1966, 20 pp. 

18. Nafziger, R. H., J. E. Tress, and J. I. Paige. Carbothermic 
Reduction of Domestic Chromites. Metall. Trans. B, v. 10B, No. 1, 
1979, pp. 5-14. 

19. Kusik, C. L., K. Parameswaram, D. J. Kinneberg, and H. V. 
Makar. Pyrometallurgical Processing Recovery of Chromium From 
Scrap Metals: Laboratory Studies. BuMines RI 8571, 1981, 41 pp. 

20. DeBarbadillo, J. J., J. K. Pargeter, and H. V. Makar. Process 
for Recovering Chromium and Other Metals From Superalloy 
Scrap. BuMines RI 8570, 1981, 73 pp. 

21. Nafziger, R. H. A Review of the Deposits and Beneficiation of 
Lower-Grade Chromite. J. S. Afr. Inst. Min. and Metall., v. 82, No. 
8, 1982, pp. 205-226. 



BuMines IC 9087: Chromium-Chromite: Bureau of Mines Assessment and Research 



77 



CARBONYL PROCESS TO UPGRADE CHROMITE CONCENTRATES 

By A. Visnapuu' and W. M. Dressel 2 



ABSTRACT 



The Bureau of Mines has upgraded domestic chromite 
concentrates by carbonyl processing. The concentrates are 
first solid-state-reduced with H 2 or CO to render the con- 
tained Fe responsive to carbonylation with CO under pres- 
sure. The carbonyl reaction occurs in two regimes, de- 
pending on whether only Fe or Fe and Cr are metallized in 
the reduction step. When only Fe is metallized during reduc- 
tion, the subsequent conversion of Fe to Fe(CO) 6 is rapid, 
and nearly all of the metallized Fe is converted. When Cr is 
metallized along with Fe during reduction, carbonyl conver- 
sion decreases rapidly with increasing Cr metallization. This 



decrease is attributed to Fe-Cr alloying by intermetallic dif- 
fusion during reduction. Controlling the chromite concen- 
trate metallization level during solid-state reduction allows 
production of upgraded chromite concentrates with diverse 
Cr 2 3 content and Cr-Fe ratios. Chromite concentrate 
response to carbonylation is presented as a function of Fe 
and Cr metallization levels. Results of a Bureau of Mines 
cost evaluation to upgrade an available Montana high-Fe 
concentrate from 42.9 pet Cr 2 3 and 1.6:1 Cr-Fe ratio to 
51.0 pet Cr 2 3 and 4:1 Cr-Fe ratio are summarized. 



INTRODUCTION 



Metals in periodic table groups VIB, VIIB, and VIII 
react with CO under certain conditions to form a series of 
volatile carbonyls with properties potentially suitable for ex- 
tractive metallurgy. A number of extractive processes 
based on the formation of metal carbonyls have been in- 
vestigated or used. Example include commercial production 
of high-purity Ni (6), recovery of Fe and Ni from lateritic 
ores (5), recovery of Fe from flotation tailings or iron oxides 
(1, 4-5, 7), production of synthetic rutile from ilmenite (9), 
and production of upgraded chromite concentrates (10-11). 
In the latter case, reduced chromite concentrates is reacted 
with CO to form volatile Fe(CO) B according to the reaction 

Fe-Cr 2 3 + 5(COXg) - Cr 2 3 + Fe(CO) 5 (g). 

Removal of some of the Fe from the concentrate increases 
the product Cr 2 3 content and Cr-Fe ratio. 

Common to all the carbonyl processes is the need to 
catalyze or promote the reaction. Sulfur or sulfur com- 
pounds have been favored for this, and were in not for the 
increase in reaction rate effected by them, commercial 
extraction of Ni and Fe as carbonyls from reduced metals 
probably would not be practical (6). Although the 
mechanism by which sulfide ions activate the metal surface 
and make it reactive is not precisely known, there is 
evidence that no more than a monolayer of the metal sur- 
face is involved. One proposed mechanism is that up to a 



monolayer the metal surface is composed of the metal and 
sulfide ions approximating the crystal habit and 
stoichiometry of the most stable sulfide. Activation is the 
result of interference with normal bonds existing on a clean 
metal, thereby producing atoms that are nearly free. In the 
presence of absorbed CO, such atoms form an activated 
metal-CO complex which then builds up into the metal car- 
bonyl. The surface remains uniformly active by continuously 
remaking the sulfide-metal bonds ruptured when metal car- 
bonyl is removed from the surface by volatilization (6). The 
other mechanism proposes that a set of intermediate metal 
carbonyl sulfides is formed that lowers the apparent activa- 
tion energy of carbonyl formation (2). In either case, a very 
small amount of S is required, and excess S hinders the 
reaction. 



1 Research physicist. 

2 Supervisory metallurgist. 

Rolla Research Center, Bureau of Mines, PO Box 280, Rolla, MO 65401. 





Abbreviations Used in This Paper 


atm 
°C 


atmosphere, standard 
degree Celsius 


g 

h 


gram 
hour 


mm 


minute 


pet 
psig 


weight percent 

pounds (force) per square inch 


St 


gauge 
short ton 


st/d 
SLM 


short ton per day 
standard liter per minute 



78 



EXPERIMENTAL PROCEDURE 



The six chromite concentrates investigated in this study 
ranged from high-Cr through high-Fe to submarginal and 
consisted of five particle size groups, as summarized in table 
1. 

Equipment, procedures, and conditions used to solid- 
state-reduce and carbonylate the chromite concentrates, 
and the optimum CO pressure, temperature, promoter 
trends, and other factors enhancing Fe(CO) 5 formation have 
been previously reported (10-11). Modifications to the 



previous procedures include multiple-charge solid-state 
reductions at different temperature zones in the small 
hydrogen reduction furnace to produce a variety of Fe 
metallization levels in the chromite concentrates. Car- 
bonylation of reduced chromite concentrates was modified 
by concurrently treating 1-g-size multiple charges in in 
dividual boats in the reactor. Promoter additions were 
based on total concentrate treated in the reactor. 



TABLE 1.— Characteristics of domestic chromite concentrate before reduction and carbonylatlon 



Concentrate 



Particle size, pet 



Analysis, pet 



Desig- 
nation 



Plus 
100 
mesh 



Minus 

100 

plus 200 

mesh 



Minus 
200 
mesh 



Cr 2 0, 



MgO 



AIA 



SIO, 



Cr-Fe 
ratio 



Montana high-Fe . . . 

California high-Fe . . 

Alaska high-Fe 

Alaska hlgh-Cr 

Alaska submarginal 



99.4 

4.4 
87.6 

5.4 











0.6 
23.4 
10.2 
23.4 


100 

100 

100 





72.2 

2.2 

71.2 
100 









42.9 
42.9 
38.2 
38.2 
42.8 
51.0 
55.0 
26.3 



18.7 
18.7 
15.1 
15.5 
19.5 
20.7 
15.6 
22.6 



11.8 
11.8 
13.3 
13.3 
12.8 
10.2 
12.4 
15.1 



16.9 
16.9 
16.5 
16.5 
23.0 
8.3 
10.1 
23.0 



1.3 
1.3 
4.5 
4.5 
1.6 
2.0 
3.2 
2.0 



1.6 
1.6 
1.7 
1.7 
1.5 
1.7 
2.4 
.8 



RESULTS AND DISCUSSION 

SOLID-STATE CHROMITE REDUCTION 



All chromite concentrates required a reductive roast to 
make them respond to carbonylation. Both H 2 and CO solid- 
state reductions were effective; but during CO reduction, 
the charge could not be cooled below 1,000° C under CO 



because of carbide formation in and carbon formation 
around the concentrate. Cooling the CO-reduced charge 
under He from the reduction temperature eliminated this 
problem. 

The chromite concentrates were reduced to various 
degrees of metallization, as summarized in table 2. The data 



TABLE 2.— Domestic chromite concentrate solid-state reduction 



(Heated to 400° C under He, 400° C through roast back to 400° C and H 2 , and 400° C to ambient under He; or heated to 400° C under He, 400° C 
through roast under CO, and roast to ambient under He. 250-g charges reduced In large furnace, and 25-g charges reduced In small furnace) 




Reduction 


Equivalent Fe 

metallization, 

pet 


Concentrate 1 


Reducing 

gas 


Temp, 
°C 


Time, 
h 


Furnace 


Weight 
loss, pet 


A 


H, 


1,100 
1,100 
1,150 
1,150 
1,200 
1,200 
1,235 
1,120 
1,155 
1,185 
1,180 
1,185 
1,045 
1,130 
1,230 
1,200 
1,045 
1,130 
1,145 
1,230 
1,185 
1,250 
1,200 
1,235 
1,300 
1,200 
1,300 
1,290 
1,200 
1,235 
1,200 
1,250 
1,300 


4 
4 
4 
16 
4 
16 
16 
16 
16 
16 
24 
40 
16 
16 
16 
16 
16 
16 
16 
16 
16 
40 
16 
16 
20 
16 
20 
16 
16 
16 
16 
16 
20 


Large 

..do 

..do 

..do 

..do 

..do 

..do 

Small 

..do 

..do 

..do 

..do 

..do 

..do 

..do 

Large 

Small 

..do 

..do 

..do 

..do 

..do 

Large 

Small 

..do 

Large 

Small 

..do 

Large 

Small 

Large 

Small 

..do 


0.64 
2.15 
2.74 
3.35 
2.79 
4.26 
5.10 
5.89 
6.43 
7.05 
7.29 
8.53 
2.36 
3.49 
4.97 
3.77 
4.21 
5.06 
5.32 
6.17 
6.74 
9.43 
3.19 
6.65 
6.90 
5.77 
9.05 
9.21 
4.65 
7.75 
6.61 
7.49 
9.09 


11 2 


B 


H, 


40.1 


C 

D 


CO 

Hj 


51.1 
62.5 
52.1 
79.5 
95.2 
109.9 
120.0 
131.6 
136.1 
159.2 
53.3 
78.6 
111.9 
84 4 




CO 

H, 


94.8 
117.1 
1,19.8 
138.9 
151 7 




c6 

Hj 


E 


H, 


212.3 
57 1 


F 


CO 

H, 


119.1 
123.5 
97 3 




cb 

Hj 


152.6 
157 5 


G 


Hj 


104 


H 


H, 


173.5 
102 1 




CO 


115.6 
140.4 



1 Designations from table 1. 



79 



represent a large number of individual reduction roasts and 
are presented to show a number of trends associated with 
precarbonylation preparation of the chromite concentrates. 
The weight lost by each concentrate is due to Fe and Cr ox- 
ides reduction, with the reduction of Fe oxides preceding 
the reduction of Cr oxides. In a study of reduction behavior 
of chromite, Searle (8) found 80 pet Fe metallization before 
any significant Cr metallization. The equivalent Fe 
metallization values are derived from weight loss on the 
assumption that the Fe is present as FeO since the Fe 2 3 
contributes only up to 25 pet of the total Fe and is reduced 
to FeO before any Fe metallization takes place. Metalliza- 
tion values in excess of 100 pet indicate definite Cr 
metallization. 

The data in table 2 show an expected increase in 
metallization with increase in roast time and temperature. 
Also evident in comparing data from concentrates A and B, 
and from CO-reduced concentrates C and D, is the increased 
metallization in the finer particle size concentrates in com- 
parison to the larger particle size concentrates. This in- 
creased metallization is attributed to shorter Fe diffusion 
distances in the smaller grains. 

Figure 1 shows four chromite concentrate photomicro- 
graphs. The natural concentrate B (fig. L4) has the pre- 
dominantly smooth, gray reflectivity of chromite. After H 2 
reduction to 51.1-pct equivalent Fe metallization (B) and to 
79.5-pct equivalent Fe metallization (C), metallic Fe ag- 
glomeration is evidenced by the appearance of the high- 
reflectivity white specks and coating on the periphery of the 
chromite grains. Concentrate D, reduced to 212.3-pct 
equivalent Fe metallization, is shown in figure ID. The 
photomicrographs show that coalescence of Fe on the sur- 
face increases with metallization, while the unreacted cen- 
tral regions (light shade in fig. IB) decrease in volume. 
Metallization begins at the surface and moves inward, with 
the Fe diffusing to the surface. As Fe metallizes and dif- 
fuses to the surface, the grain interiors become enriched in 
Cr 2 3 . The chromium oxide begins to metallize and diffuse 
to the surface when the FeO metallization is nearly com- 
plete. The larger agglomerated particles in figure ID are 
due to both Fe and Cr metallization. Photomicrographs of 
concentrates E, F, and H before and after solid-state reduc- 
tion reveal similar relationships, but the larger grain con- 
centrates, F and H, show more agglomeration in central 
regions along cracks and voids than along the periphery. 

CARBONYLATION OF REDUCED CHROMITE 
CONCENTRATES 

Research reported previously (10-11) established that 
metallized Fe in chromite concentrates reacts readily with 
CO to form the volatile Fe(CO) B . The optimum rate of Fe 
conversion to Fe(CO) 6 occurred at 140° C under 1,500 psig 
CO with the addition of small quantities of H 2 S as a pro- 
moter. The Cr 2 3 level and Cr-Fe ratio of the upgraded 
product were shown to be controlled by the degree of reduc- 
tion in the precarbonylation roast, duration of the carbonyl 
treatment, and mineralogy of the starting concentrate. The 
results reported here supplement and expand on the 
previous findings. 

A primary reason for continued interest in carbonyla- 
tion of chromite concentrates was to determine if Cr metal 
could be extracted by metallizing the Fe and Cr, converting 
both to the respective carbonyls, and separating the two by 
fractional distillation. Chromium carbonyl, Cr(CO) 6 , had 
been produced in small quantities along with Fe(CO) 6 from 
stainless steel powders, and it was surmised that it could be 



produced from chromite concentrates with sufficient Cr 
metallization. Instead, a pronounced decrease in carbonyl 
formation was observed in concentrates reduced to a level 
of complete Fe metallization and the beginning of Cr 
metallization. Further increase in Cr metallization only 
decreased the chromite concentrate response to carbonyla- 
tion. As a result of these findings, Fe extraction from 
chromite concentrates was further investigated, primarily 
as a function of Fe and Cr metallization in the concentrates. 

Table 3 illustrates this by comparing the carbonylation 
weight loss and Fe extraction percentages of concentrate B 
and D at partial Fe and no Cr metallization levels (< 100 pet 
equivalent Fe metallization) to those of total Fe and partial 
Cr metallization levels (>100 pet equivalent Fe metalliza- 
tion). The results show that during 2-h carbonylation, the Fe 
extraction passes through a maximum at about 110-pct 
metallization for concentrate B and at about 120 pet for con- 
centrate D. During 24-h carbonylation, Fe extraction ap- 
pears to improve somewhat for the higher metallization 
levels. 

The appearance of chromite concentrates shown in 
figure 1 after carbonyl processing is illustrated in figure 2. 
The natural concentrate B carbonylated without solid-state 
reduction (panel A) shows no marked difference in ap- 
pearance. When concentrate B was reduced to 51.1-pct 
equivalent Fe metallization, Fe agglomeration along the 
grain, peripheries disappeared; regions of unreacted 
chromite were still apparent as lighter shaded interior grain 
areas (B). After 79.5-pct equivalent Fe metallization, con- 
centrate B, showed no Fe or distinguished regions of 
unreacted chromite (C). Concentrate D, reduced to 
212.3-pct equivalent Fe metallization, shows dense, large 
metal particle agglomeration (D). In the latter case, Fe ex- 
traction was less than 5 pet. The agglomeration of Fe and 
Cr into large spherical particles in the more highly reduced 
chromite may be another factor, in addition to Fe and Cr 
alloying by intermetallic diffusion during reduction, that 
contributes to decrease in the carbonyl reaction rate due to 
less available metal surface area. Chromite concentrates E, 
F, and G revealed similar characteristics after carbonyla- 
tion, with voids replacing Fe in the central regions of large- 
grain concentrates F and G. 

Based on observation of decreased carbonyl conversion 
with increasing combined Fe and Cr metallization in tests 
performed to study the feasibility of extracting Cr by car- 
bonyl processing, the relationship between chromite concen- 
trate metallization and carbonyl conversion was further in- 
vestigated. Results of these studies are summarized in 
figure 3 and table 4. The studies were performed on coarse- 
and fine-particle chromites listed in table 1, reduced with H 2 
and CO to a wide selection of metallization levels, and car- 
bonylated for periods ranging from 2 to 72 h. 

Figure 3 summarizes carbonylation results on concen- 
trate B reduced up to 160-pct equivalent Fe metallization. 
Data are presented as percent of total Fe extracted from 
the concentrate for 1-g charges carbonylated for 2, 24, and 
72 h. The results show that for metallization levels up to ap- 
proximately 110 pet, the conversion of Fe to Fe(CO) B is 
practically the same for all the carbonylation times and in- 
creases linearly with increasing metallization. Above 
110-pct metallization, conversion decreases rapidly for the 
2-h treatment; Fe extracted becomes less than 5 pet at 
160-pct metallization. Concentrates carbonylated for 24 and 
72 h reach maximum conversion at 120- and 130-pct 
metallization, respectively, and then decrease at higher 
levels. At these higher metallization levels, there is a 
marked decrease in carbonyl formation rate. 



80 







FIGURE 1.— Micrographs of Montana high-Fe chromite concentrate before and after solid-state reduction (X 500). A, Natural 
concentrate B, shows a predominantly smooth gray reflectivity of the chromite grains; 8, after H 2 solid-state reduction to 51.1-pct 
equivalent Fe metallization, metallic Fe is evident by appearance of white specks along the periphery of the grains, and the 
unreduced central regions are indicated by the lighter shade; C, after reduction to 79.5-pct metallization, metallic Fe is evident as a 
coating, and central region appears reduced; and D, concentrate D reduced to 212.3-pct metallization shows agglomeration of 
large metal particles. 



81 




: 






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_ 


r- 


i 




V," •• 




" 


\\+ 


**- 


1 

i 












r '^ Jt 
...___ 


# 







FIGURE 2.— Micrographs of Montana high-Fe chromite concentrate after carbonylation (X 500). A, Natural concentrate B car- 
bonylated without solid-state reduction shows no structure change; B, carbonylated after reduction to 51.1-pct equivalent Fe 
metallization, concentrate B shows no metallic Fe but still an unreduced central region; C, carbonylated after reduction to 79.5-pct 
metallization, concentrate B shows no metallic Fe but a reduced central region; and D, concentrate D carbonylated after reduction 
to 212.3-pct metallization shows large agglomerated metal particles. 



82 



TABLE 3.— Dependence of chromite concentrate Fe extraction by carbonyl processing on equivalent Fe metallization In 

solid-state H 2 reduction 



(10-g charge 


1,500-psig CO pressure, 0.15-SLM CO flow, 140° C, 


17:1 contained Fe-H 2 S promoter mole ratio, and He purge) 




Equivalent 
Fe metal- 


Carbonylation 


Analysis, pet 


Iron 




Concentrate 1 




Weight 






lization, 
pet 


Time, 
h 


loss, 
pet 


extracted, 
pet 


Cr-Fe 




Cr 


Fe 


ratio 


B 


40.1 


2 


4.41 


31.4 


15.4 


23.1 


2.0 




62.5 


2 


8.30 


33.1 


12.0 


42.9 


2.7 




79.5 


2 


11.83 


34.8 


8.74 


60.6 


4.0 




82.9 


2 


12.51 


35.1 


8.07 


63.9 


4.4 




109.6 


2 


15.25 


36.8 


5.45 


76.8 


6.8 




119.6 


2 


12.38 


35.8 


8.67 


62.0 


4.1 




131.0 


2 


7.47 


34.1 


13.7 


37.1 


2.5 




136.1 


2 


4.94 


33.3 


16.0 


24.5 


2.1 




159.2 


2 


.31 


32.2 


20.2 


1.5 


1.6 


D 


47.4 


2 


5.79 


28.3 


10.7 


36.6 


2.7 




70.2 


2 


7.08 


29.0 


9.60 


44.3 


3.0 




97.3 


2 


11.50 


30.9 


5.31 


71.0 


5.8 




111.3 


•> 2 


13.20 


31.7 


3.58 


81.0 


8.9 




120.5 


2 


14.85 


32.4 


1.79 


90.7 


18.1 




123.2 


2 


14.63 


32.4 


2.07 


89.2 


15.7 




136.3 


2 


13.30 


32.1 


3.69 


80.6 


8.7 




151.7 


2 


7.95 


30.4 


9.41 


47.8 


3.2 




210.8 


2 


.19 


28.9 


16.9 


1.1 


1.7 


B 


40.1 


24 


4.84 


35.1 


15.0 


25.3 


2.1 




95.2 


24 


14.16 


36.0 


6.46 


71.7 


5.6 




136.1 


24 


9.81 


31.5 


11.5 


48.6 


3.1 


D 


111.3 


24 


13.87 


31.9 


2.83 


85.1 


11.3 




119.8 


24 


15.06 


32.5 


1.54 


92.0 


21.1 




151.7 


24 


14.36 


32.4 


2.64 


86.4 


12.4 




163.9 


24 


.77 


28.4 


16.1 


4.6 


1.8 




212.3 


24 


.74 


29.1 


16.5 


4.3 


1.8 



Designations from table 1. 



TABLE 4.— Dependence of chromite concentrate Fe extraction by carbonyl processing on equivalent Fe metallization In 

solid-state reduction 



(1-g multiple charges, 1,500-psig CO pressure, 0.15-SLM CO flow, 14C 


° C, 17:1 contained Fe-H 2 S promoter mole ratio, anu He purge) 




Reduction 


_ 










Iron extracted by 


Concentrate 1 


Reducing 


Weight 
loss, 


Equivalent Fe 
metallization, 


carbonylation, pet 




gas 












pet 


pet 


2 h 


24 h 


72 h 


D 


H 2 


2.11 
3.75 


47.6 
84.4 


22.7 
56.6 


29.8 
60.6 


24.0 






59.7 






4.32 


97.4 


68.9 


71.0 


74.2 






4.94 


111.2 


79.9 


84.2 


85.2 






5.36 


120.6 


86.0 


92.3 


92.3 






6.09 


137.2 


91.1 


95.2 


99.5 






6.74 


151.7 


72.7 


96.5 


99.9 






9.43 


212.3 





8.5 


24.0 


C 


CO 


.19 


4.2 


1.0 


.5 


ND 






1.37 


30.8 


16.7 


18.3 


ND 






2.08 


46.8 


27.0 


29.1 


ND 






3.49 


78.6 


51.7 


55.2 


ND 






4.97 


111.9 


61.5 


71.0 


ND 






5.44 


122.5 


19.3 


72.6 


ND 






5.65 


127.2 


7.9 . 


65.2 


ND 


D 


CO 


.69 
4.21 


15.5 
94.7 


12.0 
68.8 


11.4 
71.8 


ND 




ND 






5.20 


117.1 


84.0 


84.4 


ND 






6.17 


138.9 


92.1 


94.3 


ND 






7.15 


161.0 


10.7 


77.3 


ND 






7.42 


167.1 


14.4 


47.1 


ND 


E 


H 2 


1.67 
3.67 


29.9 
65.6 


14.8 
35.7 


15.2 
40.2 


19.8 






41.3 






4.26 


76.2 


42.4 


52.2 


51.8 






5.40 


96.6 


37.6 


61.6 


62.2 






6.49 


116.1 


15.0 


53.1 


59.7 


F 


H 2 


2.69 
6.02 


45.4 
101.5 


14.5 
54.0 


10.4 
53.3 


16.2 






59.3 






7.68 


129.5 


56.6 


78.1 


82.3 






9.34 


157.5 


15.5 


68.6 


67.7 


G 


H; 


3.83 
4.94 


85.8 
110.5 


24.0 
28.5 


30.4 
43.2 


32.8 






51.7 






7.75 


173.5 


9.5 


75.6 


80.7 


H 


H 2 


5.26 
5.83 


81.3 
90.1 


51.2 
57.8 


55.7 
58.2 


56.3 






62.6 






7.49 


115.6 


71.5 


74.8 


78.8 



ND Not determined. 



Designations from table 1. 



- 


1 1 
KEY 




i 


i 


i 




i 

o 

A 


1 
A 
A 


1 


- 


~ 


A 72 h 
O 24 h 

• 2h 










o 


• 


O 




- 












2 

• 












- 








« 








O 




- 


- 






8 










• 


A 


- 


■ 




A 
















- 


- 


• 

2 


8 












• 


O 


- 


- 


A 
8 


















- 


- o 




















- 


* 


! 1 




i 


i 


i 




1 


1 


• 
1 





20 40 60 80 100 120 140 160 ISO 

EQUIVALENT Fe METALLIZATION, pet 

FIGURE 3.— Iron extraction as a function of equivalent Fe 
metallization, H 2 -reduced Montana high-Fe chromite concen- 
trate B. One-gram multiple charges, 1,500-psig CO pressure, 
0.15-SLM CO flow, 140° C, 17:1 contained Fe-H 2 S promoter 
mole ratio, and He purge. 



Table 4 summarizes the Fe extraction results for con- 
centrates C through H. All concentrates exhibit the same 
general pattern of carbonylation response graphically de- 
picted in figure 3. The CO-reduced coarse concentrate C 
shows a decline in conversion for both 2- and 24-h carbonyla- 
tions at a lower metallization level than the CO-reduced fine 
concentrate D. Carbonylation response of the California 
high-Fe chromite concentrate, E, shows more scatter in 
data, and the maximum conversion takes place at lower 
metallization levels. This concentrate required high temper- 
ature to achieve even 120-pct metallization, even though it 
was minus 200 mesh. Carbonylation response data for the 
concentrates F, G, and H are limited, but the overall pattern 
is in agreement with that evident on other, more thoroughly 
investigated chromite concentrates. 

The Fe-to-Fe(C0)6 conversion characteristics of the 
above reduced chromite concentrates indicate that car- 
bonylation occurs in two regimes, depending on the degree 
of Fe and Cr metallization. The carbonyl reaction rate is 



rapid when only Fe is metallized, and almost all of the Fe 
converts to Fe(C0) 6 . Rapid and nearly complete Fe conver- 
sion is maintained until start of Cr metallization after ap- 
proximately 80 pet or more of the Fe is metallized. As Cr 
metallization begins and increases, carbonyl conversion ex- 
hibits a strong direct dependence on time of treatment and 
an inverse dependence on Cr metallization. This decrease in 
carbonyl reaction rate is attributed to Fe and Cr alloying by 
intermetallic diffusion during the reduction step. The alloy- 
ing effect becomes more pronounced owing to the increased 
diffusion rates at the higher roast temperatures necessary 
for more complete Cr metallization; this, in turn, inhibits 
carbonyl formation during the subsequent carbonyl treat- 
ment. Controlling the metallization pretreatment permits 
removal of some or nearly all of the Fe from chromite con- 
centrates. Thus, the Cr-Fe ratio can be adjusted to any prac- 
tical value, or a product that is nearly free of Fe can be pro- 
duced. An adverse implication is that the recovery of Cr 
metal from chromite by carbonyl technology may not be 
practical owing to the decrease in reaction rate as Cr 
metallizes and alloys with Fe. 

COST EVALUATION 

The Bureau of Mines Process Evaluation Group com- 
pleted an economic evaluation of the carbonyl process for 
upgrading chromite concentrate. The evaluation was per- 
formed specifically for concentrate B, solid-state-reduced to 
80-pct equivalent Fe metallization. During processing, 60 
pet of the contained Fe is extracted, producing an upgraded 
product that analyzes approximately 51.0 pet Cr 2 3 and 8.7 
pet Fe and has a 4:1 Cr-Fe ratio. 

The estimated operating cost and amount required to 
yield a 15-pct rate of return on investment after taxes, 
without credit for recovered Fe, is $127/st upgraded 
chromite concentrate for a plant designed to process 1,000 
st/d of concentrate feed. If the Fe is recovered and briquet- 
ted, it yields a credit of $13/st upgraded concentrate. The 
corresponding credit for Fe recovered as powder is $79. 
Some processing equipment is eliminated when Fe is re- 
covered as powder, and this reduces the operating cost and 
15-pct rate of return to $32/st of upgraded chromite. Cost 
estimates are based on an M and S equipment cost index of 
781.7. The report concludes that (1) to maximize the eco- 
nomic potential of the process, research should be concen- 
trated on the recovery of an Fe powder byproduct suitable 
for use in powder metallurgy, and (2) since no individual 
cost item dominates the process operating cost, only a major 
process modification will be likely to have a significant ef- 
fect on process economics. 



CONCLUSIONS 



Results of this study have demonstrated that chromite 
concentrates with diverse Cr-Fe ratios, Cr 2 3 content, par- 
ticle size, mineralogy, and accessory mineral content can be 
upgraded by carbonyl processing. The concentrates must 
first be solid-state-reduced with H 2 or CO. The degree of Fe 
and Cr metallization achieved in reduction controls the 
subsequent carbonylation response of the concentrate. For 
Fe-only metallization, the carbonyl reaction rate is rapid 
and conversion of metallized Fe to Fe(CO) 5 is nearly com- 
plete. As Cr metallization begins and increases, the carbonyl 



reaction rate decreases rapidly owing to Fe and Cr alloying 
by intermetallic diffusion during reduction. The product Cr- 
Fe ratio can be closely controlled by controlling the Fe 
metallization in reduction. Recovery of Cr from chromite by 
carbonyl technology may not be practical owing to the 
decrease in reaction rate at the required Cr metallization 
levels. Finer-particle-size chromite concentrates respond 
more readily to solid-state reduction, but the finer particle 
size does not improve reduced concentrate response to car- 
bonylation at the low and medium Fe metallization levels. 



84 



REFERENCES 



1. Dufour-Berte, C, and E. Pasero. Produziane di ferro da car- 
bonile in letto fluidigzato (Production of Iron Carbonyl in a Fluid- 
ized Bed). Chim. Ind. (Milan, Italy), v. 49, 1969, p. 347. 

2. Heinicke, G., N. Bock, and H. Harens. Zum Mechanismus der 
tribomechanisch aktivierten Metallcarbonylbildung unter Einfluss 
schwefelhaltiger Substanzen (Mechanism of Tribomechanical Ac- 
tivation of Metal Carbonyl Formation Under the Influence of 
Sulfur Containing Substances). Z. Anorg. Allgem. Chem., v. 372, 
1970, pp. 162-170. 

3. Lewis, R. M., J. W. Cookston, L. W. Coffer, and F. M. 
Stephens, Jr. Iron and Nickel by Carbonyl Treatment. J. Met., v. 
10, 1958, pp. 419-424. 

4. Mond, R. L., and A. E. Wallis. Researchers on the Metallic 
Carbonyls. J. Chem. Soc. Trans., v. 121, pt. 1, 1922, pp. 29-34. 

5. Okamura, T., H. Kazima, and Y. Masude. On the Synthesis of 
Iron Carbonyl. Sci. Rep. Res. Inst., Tohoku Univ., Sendai, Japan, v. 
A7, 1949, p. 319. 

6. Queneau, P., C. E. O'Neill, A. Illis, and J. S. Warner. Some 
Novel Aspects of the Pyrometallurgy and Vapometallurgy of 



Nickel. Part II - The Inco Pressure Carbonyl (IPC) Process. J. Met., 
v. 21, July 1969, pp. 41-45. 

7. Rhee, C. S. Kinetics of Formation of Iron Pentacarbonyl From 
Partially Reduced Iron Oxide. Ph.D. Thesis, Carnegie-Mellon 
Univ., Pittsburgh, PA, 1969, 305 pp. 

8. Searle, M. J., and C. W. P. Finn. The Mathematical Modeling 
of the Reduction Behavior of Chromite From the Upper Chromite 
Layer of the Bushveld Complex. Mintex Rep. M96, Randburg, 
Republic of South Africa, 1983, 21 pp. 

9. Visnapuu, A., B. C. Marek, and J. W. Jensen. Conversion of II- 
menite to Rutile by a Carbonyl Process. BuMines RI 7719, 1973, 20 
pp. 

10. Visnapuu, A., and W. M. Dressel. Upgrading High-Iron 
Chromite Concentrates by Carbonyl Processing. Paper in Process 
Mineralogy III, ed. by W. Petruk. Soc. Min. Eng. AIME, 1984, pp. 
259-274. 

11. Visnapuu, A., and W. M. Dressel. Upgrading Domestic High- 
Iron Chromite Concentrates by Carbonyl Extraction of Excess 
Iron. BuMines RI 8920, 1984, 22 pp. 



BuMines IC 9087: Chromium-Chromite: Bureau of Mines Assessment and Research 



85 



IN-PLANT RECYCLING OF CHROMIUM-BEARING SPECIALTY 
STEELMAKING WASTES 

By L. A. Neumeier 1 and M. J. Adam' 2 



ABSTRACT 



Significant amounts of Cr, Ni, and other metals are con- 
tained in furnace dusts, mill scale, and swarfs produced an- 
nually by the domestic specialty steelmaking industry. Little 
progress has been made toward in-plant recycling of these 
wastes. Bureau of Mines research has led to development of 
a process for the in-plant recovery of about 90 pet of the Cr 
and Mo and well over 90 pet of the Ni and Fe from stainless 
steelmaking electric furnace dusts, AOD vessel dusts, mill 
scale, and oily swarf. In the process, the mixed wastes are 



blended with coke breeze reductant and binder, pelletized, 
and furnace-smelted to recover the contained metals. All- 
pellet heats can be smelted, but the recommended pro- 
cedure is to charge the pellets to the production electric arc 
furnace to replace up to 20 pet of the scrap charge. A 
number of industrial-sized (19-st) commercial heats have 
been successfully made with pelletized wastes representing 
14 to 19 pet of the furnace charge. Cost evaluation indicates 
the process is economically attractive. 



INTRODUCTION 



The scrap market, for technical and economic reasons, 
has traditionally concentrated on metallic materials, with 
the low-grade dusts, fumes, solutions, and sludges being 
normally destined for landfills or other available means of 
disposal. Producers of such wastes have had little incentive 
to treat them for metals recovery. 

In the domestic specialty steelmaking industry, for in- 
stance, it is estimated that well over 20 million lb Cr and 8 
million lb Ni, plus other valuable metals, are contained in 
flue dusts, mill scale, and grinding swarfs in a typical year. 

Traditional waste handling and disposition has 
undergone a significant change over the past decade as a 
result of the passage in 1976 of the Resource Conservation 
and Recovery Act (RCRA), which is concerned with the 
"cradle-to-grave" generation, transportation, and disposal 
of hazardous waste. Chromium-bearing electric arc furnace 
dust has been categorized by the U.S. Environmental Pro- 
tection Agency (EPA) as a hazardous waste. Other par- 
ticulates are deemed hazardous if they fail the EPA's Ex- 
traction Procedure (EP) toxicity test (U). Companies that 
generate hazardous wastes are faced with much-increased 
costs of complying with regulatory standards for storing, 
transporting, and disposing of the wastes. 

One alternative to disaposal of such wastes is to develop 
improved recovery and recycling technology, which can aug- 
ment domestic supplies of critical metals such as Cr and Ni, 
as well as associated metals such as Fe and Mo. 

Research on steelmaking and other wastes has been 
conducted over a number of years by the Bureau of Mines. 
Much of the research (2-3, 6-7) involved various schemes to 
remove Zn and Pb from carbon steelmaking furnace dusts, 
using combinations of techniques such as sulfation, 
pelletization, reduction roasting, and specialized furnacing. 



Bureau recycling research (13) was also conducted on 
stainless steelmaking baghouse dusts, mill scale, and grind- 
ing swarf. Physical separation and leaching tests proved im- 
practical for segregating the metal values. The constituents 
were too intimately mixed for beneficiation separations and 
too refractory and complex for selective leaching. Acid- 
soluble constituents resulted in a high acid consumption. 
The only method showing promise involved pelletizing the 
wastes with coke breeze reductant and smelting to produce 
a master alloy. Encouraging laboratory results in this 
earlier research led to the making of a 1-st trial heat in an in- 
dustrial plant (1). 

All of these earlier heats involved all-pellet charges and 
production of master alloy ingot. Overall metal recoveries 
were deemed promising, with Cr recoveries being con- 
sistently somewhat lower than the recoveries of Ni and Fe. 
A preliminary economic evaluation was favorable. Further 
research involved initial tests of adding the pelletized 
wastes to the electric furnace in lieu of part of the conven- 
tional scrap charge (5, 8). 



1 Supervisory metallurgist (research supervisor). 
'■ Metallurgist. 
Rolla Research Center, Bureau of Mines, PO Box 280, Rolla, MO 65401. 



Abbreviations Used in This Paper 


d/wk 


day per week 


° F 


degree Fahrenheit 


h 


hour 


in 


inch 


kW-h 


kilowatt hour 


kW-h/lb 


kilowatt hour per pound 


lb 


pound 


mm 


minute 


pet 


weight percent 


St 


short ton 


st/d 


short ton per day 


yr 


year 



86 



In addition to in-plant recycling, a master alloy can be 
produced by a centralized waste processing facility. An ex- 
ample of this type of facility is the Inmetco plant of the In- 
ternational Nickel Co. (INCO), which has for the past 
several years been processing part of the stainless steelmak- 
ing dusts, mill scale, and grinding swarf being generated 
(11). The treated and smelted compositions are adjusted 
with higher grade materials to produce recyclable Fe-Cr-Ni 
ingot. 

Fosnacht (4) has recently compiled a comprehensive 
bibliography of the state-of-the-art of the processing of par- 
ticulate steelmaking wastes. 



The results reported herein represent the more recent 
efforts of Bureau research to find technically and 
economically viable recycling technology for specialty 
steelmaking wastes -to permit the return of otherwise lost 
metal values to the steelmaking circuit. An in-plant reduc- 
tion technique has been developed that results in the con- 
sistent recovery of about 90 pet of the Cr and Mo and well 
over 90 pet of the Ni and Fe from particulate stainless steel 
wastes. Description is given of the work, which began with 
small laboratory arc furnace melts, as it progressed through 
— 19-st demonstration heats at Joslyn Stainless Steels, Ft. 
Wayne, IN, under a Bureau-industry cooperative effort. 
Discussion of a cost evaluation is included. 



PROCEDURE AND RESULTS 



RAW MATERIALS 

The waste products evaluated in the research included 
electric furnace (EF) baghouse dust, argon-oxygen decar- 
burization (AOD) vessel baghouse dust, oily grinding swarf, 
and mill scale. The majority of the material was supplied by 
Joslyn Stainless Steels, and partial representative analyses 
are shown in table 1. Samples of baghouse dust and mill 
scale were also obtained from several other companies. 
Variations noted in composition of the wastes reflect varia- 
tions in the feed to the furnaces, operating procedures, 
waste collection, and product mix. 

The arc furnace and AOD vessel baghouse dusts are 
typically about 90 pet minus 400 mesh and consist essential- 
ly of complex oxides involving metals such as Fe, Cr, Ni, 
Mo, Mn, and Zn, with numerous other constituents such as 
reactive Ca, Mg, K, Na, S, Si, C, etc. Mill scale, which is ac- 
crued from blooming of heated billets, is also composed prin- 
cipally of metal oxides. Mill scale is mostly powder, but it is 
typically much coarser in particle size than baghouse dusts. 
Some larger chunks of mill scale will commonly be present. 

Swarfs result from the surface grinding of billets, slabs, 
and bars. Some of the dry swarf generated during billet 
grinding, which is less oxidized than baghouse dusts and mill 
scale, is recycled directly back to the electric furnace. The 
oily swarf used in these experiments was specifically from 
the centerless grinding of various-sized rods. It consisted of 
many small, partly oxidized fragments. It also contained ox- 
ide and carbide particles from the grinding wheels and was 
often still wet from cutting oils used as a coolant during 
grinding. The particle size of swarf is typically somewhat 
coarser than the finer fractions of mill scale. 

The coke breeze obtained from a steel plant ranged 
downward in size from about 1/4 in; it contained about 85 
pet C. The portland cement used as binder typically has a 
very fine particle size. 



LABORATORY EXPERIMENTS 

Laboratory experiments have been conducted for 
various waste mixtures using pelletizing agglomeration 
with coke breeze reductant, followed by smelting of approx- 
imately 100-lb charges in an arc furnace. 

Pelletizing 

Pelletizing was selected as the most practical and 
economic means for agglomeration of the wastes. The four 
steelmaking wastes (table 1), in proportion consistent with 
their rate of generation, were mixed with coke breeze reduc- 
tant and cement binder and blended into a composite mix- 
ture. For a plant that is collecting all four wastes, this com- 
position might typically represent some 15 pet AOD dust, 15 
to 25 pet each EF dust and mill scale, and about 40 pet 
grinding swarf. Substantial variation can, of course, be ex- 
pected. Coke breeze, added as about 10 pet to this waste 
blend, was selected as a logical C reductant because it is 
largely in a powdered condition and is an accessible source 
of C in the steelmaking industry. With a wide particle-size 
range for steelmaking wastes, a binder may be necessary, 
particularly if proportions of coarser sizes are relatively 
high. An addition of about 4 pet cement was found to be an 
effective binder for the waste mixes evaluated; the fine par- 
ticle size of the cement aids pellet formation prior to the 
hardening reaction. 

When raw coke breeze is used, it is necessary to dry it 
and crush it to pass an intermediate size screen, such as 35 
mesh, before adding it to the mixture. All mill scale was 
likewise dried, then passed through crushing rolls until > 70 
pet passed a 35-mesh screen -usually two passes through 
the rolls. Only the minus 35-mesh fraction was blended into 
the pellet mix used in smelting tests; the oversize fraction 
was saved and added with the pellets as furnace charge. A 
flow diagram of this procedure is presented in figure 1. 



TABLE 1.— Partial chemical analyses of typical stainless 
steelmaking waste products, percent 








Waste material 


Fe 


Cr 


NI 


Mo 


Mn 


Pb 


Zn 




27.8 
40.5 
61.6 
54.8 


9.3 
11.1 
11.7 

8.6 


2.2 
3.8 
6.8 
3.9 


1.1 
.7 

1.2 
.5 


3.6 

5.5 

1.0 

.8 


0.8 
.6 

.1 
.1 


4.9 


AOD vessel dust 

Grinding swarf 


.8 
<.1 
<.1 



87 



Coke breeze Cement 

(minus 35-mesh) 4 pet 

10 pet 



Electric 

furnace 

dust 

17 pet 



AOD 
dust 
12 pet 



Grinding 
swarf 
40 pet 



Mill scale 
17 pet 



I 



Blender 



-Minus 35-mesh- 



Screen - 
3/4 -in 
35 -mesh 



Plus 35-mesh 



Pel letizer 



Air dry 24 h, 
oven dry 6 h, 250° F 



Roll crusher- 
2 passes 



Plus 3/4-in 



Screen - 
35-mesh 



Plus 35-mesh 



Finished pellets 



Mill scale 



FIGURE 1.— Flow diagram for laboratory agglomeration of four stainless steelmaking wastes by pelletizing with coke breeze 
reductant and cement binder. Pellets of somewhat reduced but generally adequate strength can also be produced by air drying 
only. 



Pellets of the four-waste mixture were made in a 36-in- 
diam drum pelletizer and required the addition of about 12 
pet water to the blended mix in order to form 3/8- to 3/4-in- 
diam pellets. The pellets were first air-dried for 24 h, then 
oven-dried at 250° F for 6 h. Drying at higher temperatures 
tended to result in spalling. The pellets had 5- to 30-lb 
crushing strength, which was sufficient for the limited 
amount of handling required. When the wastes listed in 
table 1 were mixed in the indicated proportion and pelletiz- 
ed, the resultant pellets plus oversize mill scale analyzed 
roughly 10 pet Cr, 4 pet Ni, and 1 pet Mo. 

Experience has shown that it is not always necessary to 
oven-dry the pelletized waste mix. Most of the laboratory 
heats made in the latter part of the testing program were 
made using pellets that were air-dried only. The ex- 
periments included adding pellets to the furnace that were 
only 2 h old and very wet. These were rolled at a uniform 
rate down a conveyor and dropped through the furnace top 
onto the melt surface. As much as 13 pet of the melt charge 
(the most tried) was added in this manner without problem. 

Other efforts were made to simplify the pelletizing pro- 
cedure. For some trials, the cement binder was eliminated 
from the pellet mix to decrease slag volume. No difficulty 
was encountered in making pellets; however, after storage 
for several weeks, the pellets tended to spall and powder. 
For extended storage, some binder appears necessary. Add- 
ing 1 to 2 pet bentonite resulted in acceptable pellets that 
were stable for longer periods than when no cement was ad- 
ded. It was found that the mill scale could be crushed and 



screened through 20-mesh or even 10-mesh (rather than 
35-mesh) screens with no apparent effect on pellet proper- 
ties. 

Arc Furnace Smelting of Stainless Steelmaking 
Wastes 

Earlier tests in an induction furnace (IS) indicated that 
numerous combinations of pellet compositions could be 
smelted, with the C in the coke breeze reducing essentially 
all the oxides of Fe and Ni and about half of the Cr oxide. It 
was observed that ferrosilicon could then be added to the 
molten bath to scavenge much of the remaining Cr from the 
slag. 

The procedure for the 100-lb arc furnace melts began 
with preheating the furnace refractories for 1 h, followed by 
charging 90 to 95 lb of pellets over a 45-min period. The 5- to 
10-lb portion of loose (plus 35-mesh) mill scale was then 
added, and the furnace temperature was brought to at least 
2,950° F. At this point, 3.0 pet Si, as ferrosilicon (75 pet Si), 
was added to the melt and stirred vigorously to enhance 
mixing and effect additional reduction of Cr oxide from the 
slag. The melt was allowed to reach 2,950° to 3,100° F 
before tapping. The ingots accounted for about a 60-pct 
metal yield from the wastes charged. The slag represented 
some 10 to 15 pet of the original charge weight. 

Further laboratory testing indicated that 0.3 pet Al (as a 
percentage of charge weight), added as shot, accomplished 
roughly the same amount of reduction as 3.0 pet Si. Table 2 



88 



shows results of tests comparing the use of Fe-Si, Fe-Si-Al, 
and Al. Other heats were made without Si or Al reductants; 
the melts were held similarly for 20 to 30 min before tap- 
ping, within the range 2,850° to 3,050°F. Only those held 30 
min at 3,050°F showed improved Cr recovery relative to 
that for the lower temperatures. The reduction of the Cr ox- 
ide is related to time and temperature, as well as the type 
and amount of reductant. 

Some stainless producers had indicated that they had 
been stockpiling mill scale. Samples were obtained from five 
companies. Partial analyses are shown in table 3. The scale 
from company C originated from ferritic stainless produc- 
tion; the others were from austenitic stainless production. 
The mill scales were mixed with other wastes and pelletized 
in two approximate compositions, as shown in table 4. 

The values are arbitrary, but those for the "low" scale 
composition are intended to represent an approximate 
generation rate in a plant producing and segregating all 
four wastes. The "high" scale composition reflects a situa- 
tion wherein stockpiled mill scale would be used up at a 
faster-than-generated rate. Small-scale pelletizing tests in- 
dicated that pellets containing as much as 55 pet mill scale 
could be made, but 35 pet was a more practical value from 
the standpoint of a higher proportion of fines present and 
better pellet formation and strength. 

The mixtures were prepared, blended to the composi- 
tions shown for low and high mill scale, and arc-furnace- 
melted as described previously. The slag was reduced with 
ferrosilicon. The results obtained from the group represent- 
ing "low" mill scale (17.4 pet) pellets are shown in table 5. 

It should be noted that laboratory smelting tests in- 
volved a charge consisting of 90 to 95 pet pellets and 5 to 10 



pet loose mill scale. Some producers might have furnace 
capacity available to intermittently melt all-pellet charges 
for metering of hot metal to production heats. This method 
could also help reduce large backlogs of wastes. However, in 
normal industrial practice, it is anticipated that only 10 to 20 
pet of the furnace charge would consist of pelletized wastes, 
to replace a portion of the scrap charge. This is the most 
economical and least energy-intensive approach and can 
readily match or exceed waste generation rates. Excess 
reductant normally available in production heats can also 
assist metal recoveries from the wastes. Under these cir- 
cumstances, the slag generation would not be as much as in- 
dicated for the heats in table 5 but should be near to, 
although perhaps toward the high end of, normal ranges. 

The experiments with pelletized mill scale indicated that 
82 to 92 pet of the Cr could be readily recovered. Additional 
reductant and/or additional heating would increase the 
recoveries. Nickel recovery was, as expected, much higher. 
The results of the melting trials on "high" mill scale (35.0 
pet) mixtures indicated a Cr recovery 5 to 10 pet lower than 
for "low" (17.4 pet) mill scale mixtures. This was due, at 
least in part, to the fact that the higher mill scale content 
resulted in a somewhat greater slag volume; that is, even 
with the same Cr slag solubility per unit volume, more total 
Cr partitioned to the higher volume slag. 

With other factors being equal, the Cr solubility in slag 
decreases with increased slag basicity (12), with slag basicity 
being defined as the ratio of percentage CaO plus MgO to 
Si0 2 . The increased slag volume and weight brought about 
by the increased lime addition needed to increase the basici- 
ty may, however, offset any gain in reduced Cr solubility 
when considering the total Cr in the slag. 



TABLE 2.— Recovery of Fe, Cr, and Ni from pelletized wastes after the smelting addition of various reductants 1 







Ingot ana 


lysis, pet 




Recovery, pet 


Metal recovered 


Reductant added, pet 


Fe 


Cr 


Ni 


Si 


Fe 


Cr 


Ni 


pet of charge 


3 Si 2 


61.9 
69.6 
69.9 


14.2 
15.1 
15.5 


7.1 
6.9 
7.1 


6.9 
2.3 

.7 


85.3 
97.1 
99.9 


91.5 
84.7 
93.4 


99.3 
90.5 
97.8 


64.6 


0.6 Si, 0.3 Al 3 


58.2 


0.3 Al 4 


61.8 



'In addition to the 10 pet coke breeze reductant in pellets. 

! As ferrosilicon (75 pet Si) 

3 As Al-containing ferrosilicon (20 AI-40 Fe-40 Si). 

'As Al shot. 



TABLE 3.— Partial analyses of stainless steel mill scale samples, 
percent 



Company 










designation 


Fe 


Cr 


Ni 


Mo 


A 


54.8 


8.6 


3.9 


0.48 


B 


51.9 


11.2 


7.0 


.47 


C 


62.7 


7.6 


.5 


.22 


D 


49.4 


8.4 


3.7 


.16 


E 


56.2 


9.1 


3.0 


.66 



TABLE 4.— Composition of pellets with low and high mill scale 
content, percent 



Component 


Low mill 
scale 


High mill 
scale 




17.4 
17.4 
13.0 
39.1 
8.7 
4.4 


35.0 


EF dust 

AOD dust 


12.6 
9.5 


Grinding swarf 

Coke breeze 


28.0 
10.5 
4.4 






Total 


100.0 


100.0 



TABLE 5.— Results of smelting pelletized waste mixtures containing mill scale 1 obtained from five stainless steel producers 



Company 


Ingot analysis, pet 


Recovery, pet 


Ingot as 
pet of charge 


Slag as 


designation 


Cr 


NI 


Mo 


Cr 


Ni 


Mo 


pet of charge 


A 
B 
C 
D 

E 


16.0 
16.1 
14.5 
14.9 
14.9 


7.2 
7.7 
5.9 
7.1 
6.2 


1.00 
.80 
.79 
.83 
.92 


92.6 
87.7 
86.1 
82.3 
93.0 


100.0 
90.7 
97.9 
93.2 
99.0 


74.5 
91.9 
91.5 
63.6 

100.0 


60.0 
47.9 
56.9 
55.9 
63.4 


14.0 
13.0 
16.9 
19.3 
19.0 



M7.4 pet mill scale in the pellets; other ingredients were (In pet) 17.4 EF dust, 13.0 AOD dust, 39.1 grinding swarf, 8.7 coke breeze, and 4.4 cement. 



89 



It remains to be conclusively demonstrated to what ex- 
tent some of the minor metals such as Zn and Pb in the elec- 
tric furnace dust will build up in the baghouse dust with 
repeated pelletizing and refurnacing. The longer term con- 
centration of minor elements (rate and extent) in recycled 
furnace dust will not be clarified until results are reported 
for campaigns extending over a substantial number of 
heats, with careful analysis of all charge and product 
materials. 

Some extended campaigns have been made to recycle 
baghouse dusts to the furnace without added C or other 
reductant, with the main objective being to dispose of haz- 
ardous waste by slagging as an alternative to landfilling, 
rather than gaining metal recovery. One firm has been 
recycling pelletized minimill carbon steelmaking furnace 
dust in this manner (10). Even without reductant added with 
the pellets, some increased Fe yield has apparently been 
realized in these instances, evidently by supplying some 
"equilibrium" slag Fe oxide requirements from the furnace 
dust rather than by Fe oxidation from the melt. Some 
limited reduction may be expected from excess reductant (Si 
and C) present in the melt. For further information on the 
composition and nature of carbon and stainless steelmaking 
furnace dusts, the reader is directed to the comprehensive 
arc furnace dust program conducted by Lehigh University 
and the Bureau of Mines, with U.S. Department of Com- 
merce funding, under AISI collaboration and coordination 
(9). 



LARGE-SCALE DEMONSTRATION HEATS 
All-Pellet Heats 

The procedures derived in the laboratory experiments 
were tried on a larger scale in the form of a 1-st heat of the 
pelletized waste mixture (1), which was made by Union Car- 
bide Corp., Niagara Falls, NY. When it was evident that 
recoveries from this heat were sufficiently good, plans were 
formulated for substantially larger scale industrial trials. 

The first of these large-scale demonstration trials was 
an all-pellet heat of approximately 12.5 st made in the pro- 
duction plant of Joslyn Stainless Steels. The wastes, 
generated during normal operations at Joslyn, were pellet- 
ized by a contractor in accordance with specifications 
developed at the Bureau's Rolla Research Center. The 
pellets ranged from 3/8- to 1-in diam and represented the 
mixture indicated earlier as "low" (17.4 pet) mill scale. The 
pellets analyzed 42.5 pet Fe, 9.6 pet Cr, 4.0 pet Ni, and 0.7 
pet Mo. 

The charge to the furnace consisted of approximately 
20,900 lb pellets and 1,100 lb oversize mill scale along with 
0.5 st lime. Several hundred pounds of steel punchings had 



been added at the outset to help strike an arc. When the 
charge was fully molten, the melt was sampled over a 
30-min period. An addition of 1,320 lb ferrosilicon (50 pet Si) 
was made to reduce Cr oxide remaining in the slag. Im- 
proved contact between the ferrosilicon and slag was 
achieved by stirring with an argon lance. The melt was tap- 
ped through the slag into a ladle from which it was poured 
into 14- by 14-in molds. The master alloy ingot produced 
weighed 12,300 lb and analyzed, in pet, 76.7 Fe, 11.8 Cr, 6.5 
Ni, 0.8 Mo, 0.9 Mn, 4.3 Si, and 3.2 C. These values 
represented recoveries of (in pet) 86.1 Fe, 68.7 Cr, and 92.0 
Ni. As shown in table 6, power consumption was 1.05 
kW-h/lb of metal tapped. 

The Cr recovery was lower than that experienced in 
smaller scale tests but was considered good for a "one-shot" 
experiment. Temperature was probably responsible for the 
lower recovery. After the ferrosilicon addition, the bath 
temperature of 2,750° F was some 200° F below the 
temperature of most of the laboratory heats. Nevertheless, 
Ni, the metal of highest total value, reported to the ingot as 
expected. 

An 8,000-lb portion of the master alloy ingot from the 
all-pellet heat was incorporated into a commercial 19-st heat 
(heat 2, table 6) of type 316 stainless steel. The master alloy 
was completely compatible with the balance of the charge, 
principally stainless scrap. The heat was completed within 
the expected time, power consumed was normal, and there 
were no problems in either the arc furnace melting or AOD 
refining. The remainder of the ingot material was used in 
another commercial heat with equally good results. 

Pellet-Plus-Scrap Heats 

At this point, rather than optimizing the making of all- 
pellet heats, it was decided to go directly to the overall 
simpler and more economical introduction of waste pellets 
into the production arc furnace in lieu of part of the normal 
scrap charge. It was judged that the advantages of this ap- 
proach would be (1) lower energy consumption, (2) simpler 
processing without intermediate master alloy ingot requir- 
ing remelting, and (3) variation of the quantity and composi- 
tion of waste pellets as dictated by needs. It was realized 
that careful attention would have to be given to the furnace 
charge to accommodate the pellet waste ingredients and 
their products. However, since the makeup of furnace 
charges is commonly computer calculated, programs can be 
readily adjusted to account for this unconventional raw 
material. 

Two heats were made with the remaining pellets from 
the Joslyn all-pellet heat and are hereafter referred to as 
'low-scale" pellets. Tonnage quantities of pellets also were 
produced by a contractor with substantially augmented 
percentage of mill scale. This "high-scale" composition was 



TABLE 6.— Comparison of charge weight, metal tapped, and energy requirements for Joselyn demonstration heats 1 (all pellet) 

and 2 (master alloy) 





Type of heat 


Charge, lb 


Waste, pet 


Metal 
tapped, lb 


Power 


Heat 


Total 


Waste 


consumption,' 


1 
2 


All pellet 

Scrap plus heat 1 master alloy . . 


25,385 
42,025 


22,010 
7,980 


86.7 
19.0 


12,320 
39,700 


1.05 
.254 



'Per pound of metal tapped. 



90 



TABLE 7— Comparison of charge weight, metal tapped, and energy requirements for Joslyn demonstration heats 3 to 7 

(pellets partly replace scrap) 



Heat 


Type of heat 


Charge, lb 


Waste, pet 


Metal 
tapped, lb 


Power con- 
sumption,' kW-h 






Total 


Waste 


Tap temp, °F 


3 
4 
5 
6 
7 


Scrap plus "low-scale" pellets . . 

..do 

Scrap plus "high-scale" pellets . 

..do 

..do 


41,790 
41,600 
41,940 
43,490 
42,900 


5,970 
7,870 
6,300 
6,250 
8,200 


14.3 
18.9 
15.0 
14.4 
19.0 


38,500 
36,500 
38,000 
36,600 
36,300 


0.244 
.260 
.263 
.259 
.261 


2,920 
2,960 
3,000 
2,950 
2,940 



1 Per pound of metal tapped. 



TABLE 8.— Recovery of Cr, Ni, and Mo from commercial pellet- 
plus-scrap heats 3 to 7, percent 



Heat 


Type of heat 


Cr 


NI 


Mo 


3 


Scrap plus 14 pet "low-scale" pellets . . 


93.0 


99.7 


99.9 


4 


Scrap plus 19 pet "low-scale" pellets . . 


93.7 


89.7 


95.0 


5 


Scrap plus 15 pet "high-scale" pellets . 


97.3 


99.1 


93.2 


6 


Scrap plus 14 pet "high-scale" pellets . 


90.8 


91.9 


82.8 


7 


Scrap plus 19 pet "high-scale" pellets . 


91.4 


92.3 


84.5 



tested to simulate consumption of substantial quantities of 
stockpiled mill scale. The makeup of the "high-scale" pellets 
follows: 



Mill scale 

EF dust 

AOD dust 

Grinding swarf . 
Coke breeze . . . 
Cement 



Pet 
30 
13 

9 
33 
11 

4 



The pellet composition (including oversize mill scale) was, in 
pet, 39.2 Fe, 8.9 Cr, 3.7 Ni, and 0.5 Mo. 

Five type 316 stainless steel heats were made in a 19-st 
production furnace, in which pelletized wastes constituted 
14 to 19 pet of the nominal charge. The pellets were added 
to the arc furnace concurrently with the stainless scrap, 
making it unnecessary to backcharge. In all heats, only that 
quantity of ferrosilicon normally added to "quiet" such scrap 
melts was added. This ranged from to 300 lb. The slag 
volume in each case was considered within the normal range 
for production heats. (With an extended campaign, some in- 
creased slag volume can be expected when partly replacing 
relatively clean scrap with pelletized wastes, other factors 
being equal.) Pertinent statistics from the five heats are 



presented in table 7. All heats met required specifications 
after processing through the AOD vessel and were 
marketed as commercial bar, rod, or forging ingot. Table 8 
gives the recoveries of Cr, Ni, and Mo, which, on the 
average, were considered equivalent to the customary 
values for all-scrap heats. Iron recoveries were consistently 
substantially > 90 pet. 

Metal Value of Pelletized Wastes 

Technically and mechanically, this recycling scheme has 
been shown to work well. The question naturally arises as to 
whether it is also economical. The Bureau completed inter- 
nal studies of capital and operating costs for a plant addition 
producing pellets from wastes such as flue dusts, mill scale, 
and/or oily swarf. The cost for a 15-st/d pelletizing capacity 
was estimated at $1,004,000 for oven drying of pellets and 
$554,000 for air drying. Estimated operating cost based on 
1-shift-per-day, 5-d/wk operation (20-yr life) was estimated 
at about $122/st for oven drying and $46/st for air drying. 

This can be contrasted to the contained value of the Cr, 
Ni, and Mo in the pellets. The value depends on the current 
price of ferroalloys or of appropriate scrap, particularly 
stainless steel (18 Cr-8 Ni) scrap. A charge is sometimes ad- 
ded for iron units, but this has not been the case with the re- 
cent relatively depressed scrap market. On the basis of only 
Cr, Ni, and Mo for a waste mixture similar to that employed 
in the trials at Joslyn Stainless Steels (low mill scale), with 
approximate contained metal values of $0.42/lb for Cr, 
$3.18/lb for Ni, and $4.60/lb for Mo (mid-1984 ferroalloy 
contained-metal values), the pellets would have a value of 
over $390/st. Deducting the net operating cost of some 
$122/st for oven drying or $46/st for air drying indicates a 
net gain of some $0.13 or $0.17/lb, respectively -a signifi- 
cant economic potential. 



CONCLUSIONS 



It has been shown that stainless steelmaking wastes such 
as flue dusts, mill scale, and grinding swarf can be pelletized 
and reduced in the arc furnace as a means of recovering the 
contained scarce and valuable metals, while coincidentally 
solving problems of storage and waste disposal. The 
recovery procedure utilizes the reduction of metal oxides 
with C during the arc furnace melting, followed by a 
scavenging slag reduction of additional Cr oxide with fer- 
rosilicon or Al. 

One variation of the processing involves preparation of 
all-pellet smelting heats to produce master alloy ingot for 
recycle. This may be appropriate if furnace capacity is 
available in slack periods and large waste backlogs exist. 



Alternatively, and recommended as being more 
economical, the waste-bearing pellets can be added directly 
to the arc furnace as some 10 to 20 pet of the total charge 
for production heats in lieu of part of the usual scrap or alloy 
charge required. The addition rate will depend on factors 
such as the rate of waste generation, waste backlog ac- 
cumulation, and alloy product mix at a particular plant. 

The dusts, scale, and swarf can be mixed and pelletized 
with little difficulty, providing both a means for adding C to 
the mix and a vehicle for charging to the furnace. Numerous 
varied combinations of pellet mix have been shown to be 
possible. Only conventional equipment is needed for ag- 
glomeration. 



91 



Usual recoveries of substantially greater than 90 pet of 
the Ni and Fe have been attained, and some 90 pet of the Cr 
and Mo appear consistently recoverable with proper control 
of variables. Other metals such as Mn are coincidentally 
recovered. Conventional arc furnaces were used throughout 
the testing. 

The fact that this technology is readily transferable to 
an industrial scale was shown by the successful making of a 
number of demonstration heats ranging in size from 12.5 st 
for an all-pellet heat to about 19 st for a series of pellet-plus- 
scrap heats. The master alloy ingot from the all-pellet 
demonstration heat was used to make commercial stainless 



steel products without difficulty. No problems were en- 
countered in the commerical stainless production heats to 
which up to 19 pet pellets were added in lieu of the normal 
scrap charge. 

When the particular waste combination outlined in this 
report is pelletized for recycle as a scrap substitute charge 
material, the pellets have a net value of more than $0.13/lb 
for oven drying or $0.17/lb for air drying, which implies an 
economically viable process. 

Test results also indicate that a wide compositional 
variation of specialty steelmaking wastes can be incor- 
porated into pellets for furnace charging. 



REFERENCES 



1. Barnard, P. G., W. M. Dressel, and M. M. Fine. Arc Furnace 
Recycling of Chromium-Nickel From Stainless Steel Wastes. 
BuMines RI 8218, 1977, 10 pp. 

2. Barnard, P. G., A. G. Starliper, W. M. Dressel, and M. M. Fine. 
Recycling of Steelmaking Dusts. BuMines TPR 52, 1972, 10 pp. 

3. Dressel, W. M., P. G. Barnard, and M. M. Fine. Removal of 
Lead and Zinc and the Production of Prereduced Pellets From Iron 
and Steelmaking Wastes. BuMines RI 7927, 1974, 15 pp. 

4. Fosnacht, D. R. Recycling of Ferrous Steel Plant Fines: State- 
of-the-Art. Iron and Steelmaker, v. 8, No. 4, April 1981, pp. 22-26. 

5. Higley, L. W., Jr., R. L. Crosby, and L. A. Neumeier. In-Plant 
Recycling of Stainless and Other Specialty Steelmaking Wastes. 
BuMines RI 8724, 1982, 16 pp. 

6. Higley, L. W., Jr., and M. M. Fine. Electric Furnace Steelmak- 
ing Dusts-A Zinc Raw Material. BuMines RI 8209, 1977, 15 pp. 

7. Higley, L. W., Jr., and H. H. Fukubayashi. Method for 
Recovery of Zinc and Lead From Electric Furnace Steelmaking 
Dusts. Paper in Proceedings of the Fourth Mineral Waste Utiliza- 
tion Symposium. IIT Res. Inst., Chicago, IL, 1974, pp. 295-302. 

8. Higley, L. W., Jr., L. A. Neumeier, M. M. Fine, and J. C. Hart- 
man. Stainless Steel Waste Recovery System Perfected by Bureau 
of Mines Research. 33 Metal Producing, Nov. 1979, pp. 57-59. 



9. Lehigh University. Characterization, Recovery and Recycling 
of Electric Arc Furnace Dusts. Final report prepared for U.S. Dep. 
Commerce under Project 99-26-09885-10, Feb. 1982, 313 pp.; NTIS 
PB 82-182585. 

10. Mueller, C. P. Recovery of Metallics From Specialty Steel 
Slags and Wastes. Pres. at AISI Symposium on Recovery of Alloys 
From Specialty Steel Wastes, Pittsburgh, PA, Oct. 21-22, 1981; in- 
formation available from International Mill Service, Inc., 
Philadelphia, PA. 

11. Pargeter, J. K. Operating Experience With the Inmetco Pro- 
cess for the Recovery of Stainless Steelmaking Wastes. Paper in 
Proceedings of the Seventh Mineral Waste Utilization Symposium. 
IIT Res. Inst., Chicago, IL, 1980, pp. 118-126. 

12. Peckner, D., and I. M. Bernstein. Handbook of Stainless 
Steels. McGraw-Hill, 1977, pp. 3-1 to 3-35. 

13. Powell, H. E., W. M. Dressel, and R. L. Crosby. Converting 
Stainless Steel Furnace Flue Dusts and Wastes to a Recyclable 
Alloy. BuMines RI 8039, 1975, 24 pp. 

14. U.S. Environmental Protection Agency. Hazardous Waste 
Regulations. Federal Register, v. 45, No. 98, 1980, p. 33127. 



MATERIALS SESSION 

Chairman: Howard W. Leavenworth, Jr. 

Research Supervisor 

U.S. Bureau of Mines 

Albany Research Center 

P.O. Box 70 

Albany, OR 97321 



BuMines IC 9087: Chromium-Chromite: Bureau of Mines Assessment and Research 



95 



AN OVERVIEW OF CHROMIUM NEEDS AND USES 

By Howard W. Leavenworth, Jr. 1 
ABSTRACT 



The importance of maintaining viable ferrochromium 
and stainless steel industries in the United States is stressed, 
as is the need for developing substitute materials for those 
containing large quantities of Cr, including superalloys, 
refractories, and coatings as well as stainless steels. The 
availability of Cr-free substitutes for superalloys would 



make the United States stronger, but the most urgent need 
is for improvements in scrap identification and recycling 
and in near-net-shape technology. The need to make Cr- 
bearing materials last longer in service through research on 
wear and corrosion also is emphasized. 



INTRODUCTION 



One purpose of this presentation is to provide an over- 
view of the many uses for Cr . Another purpose is to serve as 
an introduction to the materials session that deals with Cr 
as an alloying element either in coatings or in new alloys 
that contain less Cr than do the materials they are designed 
to replace in the event of a disruption of Cr supplies. 

Topics in the session will also include Cr usage in wear- 
resistant materials and in refractories. Wear represents 
more than $100 billion annual loss to our economy, and it is 
an especially serious problem in the mining industry, where 
strategic metals, such as Cr, are used in large machinery. 
Figure 1 shows worn-out cone crushers near a mine in Col- 
orado. The stack of cones shown here represents less than a 
1-yr supply. They also represent a loss of strategic metals 



unless that material is recycled. Dr. Blickensderfer will have 
much to say to us on the subject of wear. 

Mr. Arthur Petty will talk to us about refractories. Of 
the Cr ore that was imported into this country from 1979 to 
1983, 17 pet (1) was used for making refractories. Mr. 
Petty"s research deals with lowering the Cr content of 
refractories, used mainly for making refractory brick to line 
metallurgical furnaces. 



1 Supervisory metallurgist, Albany Research Center, Bureau of Mines, 
P.O. Box 70, Albany, OR 97321. 





Abbreviations Used in This Paper 


lb 
mt 
pet 
st 


pound 
metric ton 
weight percent 
short ton 


yr 


year 



96 




FIGURE 1.— Worn cone crusher liners. 



CHROMIUM USAGE 



As discussed earlier by Dr. John Papp, the chromium 
commodity specialist for the Bureau of Mines, Cr has a wide 
range of uses in three primary consumer groups: refrac- 
tories, chemicals, and metals and alloys. 

In 1978, the National Academy of Sciences published an 
NMAB report entitled "Contingency Plans for Chromium 
Utilization" (2). Table 1 in that report summarized the 
potential savings of Cr by substitution and an estimate of 
the time to conduct necessary research and development ac- 
tivities. Particularly interesting is the amount of Cr that 
was identified as "irreplaceable," 35 pet of the total or 40 pet 
of that used in metallic alloys. The conclusion that this much 
Cr is irreplaceable was based on "current state of 
knowledge." The NMAB publication was invaluable, and it 
still is today, but this conference will supplement that report 
by showing that more Cr can be saved through substitution 
than was realized 7 yr ago. 

The most critical use of Cr from a national defense point 
of view is in the making of superalloys for airplane engines 
(or in actuality, for making scrap). The weight of semifin- 
ished superalloy products shipped is only one-third of the 
weight of the alloy melted (3). In fact, some complex ma- 
chined components may have a final product yield of less 
than 10 pet. The 14,030 lb of materials that go into making 
an engine for a modern fighter plane are listed in the cap- 
tion of figure 2. This engine weighs only about 3,000 lb, 2 so 
it is evident that much of the Cr and other strategic alloying 
elements are not utilized efficiently. Therefore, if the Cr 
that goes into making airplane engines is to be conserved, 
not only should the technology of recycling superalloy scrap 
be continually updated, but it would be more productive to 
concentrate on lowering the production of scrap. The latter 
can be done by near-net-shape technology. 

As is well known, the Bureau of Mines has conducted 
research on recycling for many years. Mr. Leander 
Neumeier will talk about recycling stainless steel making 
wastes. As far as superalloys are concerned, the Bureau 



z Discussion between the author and engineers at Pratt and Whitney Aircraft 
Co., East Hartford, CT. 



contracted for studies on them several years ago (4-5), and 
now scientists at the Bureau's Avondale (MD) Research 
Center are working on various scrap identification techni- 
ques, including one based on specific characteristics of 
sparks emitted by a simple grinding procedure. 

The use of Cr for making the superalloys that go into 
airplanes is obviously important, but that is not the greatest 
usage for this critical and strategic metal. Stainless steels 
typically account for 70 pet of the metallurgical-grade Cr 
imported into the United States (6). 

The consumption of Cr ferroalloys, metal, and other Cr- 
containing materials by end use follows: stainless and heat- 
resisting steel, 81 pet; full-alloy steel, 9 pet; superalloys, 3 
pet; and other alloys, 7 pet. In 1984, estimated Cr contained 
in purchased stainless steel scrap amounted to 18 pet of Cr 
demand (7). This shows that some progress is being made in 
recycling Cr-containing materials, because only 9 pet was 
recycled in 1980 (8). Nevertheless, improved recycling 
technology is needed, particularly for obsolete and con- 
taminated special alloy scrap and waste. 

Stainless steels are made from scrap and fer- 
rochromium, not Cr metal. In 1960, 92 pet of all ferroalloys 
consumed in the United States were domestically produced. 
By 1970, that figure was down to 86 pet; by 1980, it was 
down to 55 pet; by 1981, it was down to 45 pet; and by 1982, 
it was at 35 pet (7). The point is, the United States has not 
been importing chromite ore; domestic steel plants have 
been importing ferroalloys. Domestic smelters have not 
been able to compete with modern smelters located close to 
Cr ore fields. Ferrochromium production costs, which in- 
clude power, labor, and transportation, are lower in coun- 
tries where Cr ore is mined than they are in the United 
States (9). Also, national policies in the producer countries 
often provide economic incentives for local processing of 
ferroalloys. But these advantages are not insurmountable, 
and they may not last much longer. 

The growing need to blend together ores that have dif- 
ferent chemical and physical properites means that all pro- 
ducers will need to import ores. Eventually all producers 
will pay the additional cost of transporting ore (10). Labor 



97 




FIGURE 2.— The metals that go into making an engine for a modern fighter plane include 5,366 lb Ti, 5,204 lb Ni, 1,656 lb Cr, 910 
lb Co, 720 lb Al, 171 lb Cb, and 3 lb Ta. Most of these materials are lost during machining. 



rates in many producer countries are low now, but are likely 
to increase rapidly, thereby narrowing the cost advantages 
of foreign labor. If U.S. industry can improve its furnaces to 
reduce energy consumption and automate our processing, 
there is a good chance to revitalize the ferrochromium in- 
dustry in this country. 

Evidently the Federal Government does not want to 
lose this vital industry. In 1982, domestic ferrochromium 
producers were given the opportunity to process up to half 
of the General Services Administration (GSA) chrome ore 
stockpile over a 10-yr period (10). In 1984, the 
Undersecretary of Defense for Research and Engineering, 
Richard DeLauen, signed a Government procurement policy 
requiring defense contractors to buy high-C ferrochromium 
only from U.S. producers even though there was no ongoing 
domestic production at the time of signing. Mr. DeLauen 
emphasized that ferrochromium "is our most critical 
material -period." He noted that the national defense 
stockpile held nearly 2.5 million st Cr ore "which would be 
worthless in an emergency situation if there were no way to 
convert it to ferrochromium, an essential ingredient in 
special grades of steel" (11). More recently, the GSA pro- 
posed a "Buy America" clause in the Federal Government's 
procurement code, requiring that all purchases of Cr for 
stockpile purposes be made from the domestic industry(i2). 

On the suject of ferrochromium, an unusual trend has 
started in Japan and Europe. The Ministry of International 
Trade of Japan (MITI) is requiring that ferrochromium 
manufacturers reduce capacity by 10 pet by 1988 (18). This 
MITI action is a departure from the traditional Japanese 
trade position of importing raw materials and exporting 
finished goods. 

Shutdowns have been common in the ferrochromium in- 
dustry, but what about the steel industry? The capacity of 
the United States to produce stainless steel ingots from 
scrap and ferrochromium is about 2 million mt. That max- 
imum capacity was almost reached in 1974 and 1979, as 
shown in figure 3. However, note that both Japan and the 
European Economic Community (EEC) exceed domestic 
capacity. Japan has reduced its steel exports, and most steel 
exports from the EEC are being restrained by a 1982 agree- 
ment. Actually, these restraining agreements only increased 
imports from Canada and from developing countries such as 
Korea, Mexico, and Brazil. The point being made here is 
that the United States has actually gone beyond the point of 




I960 1970 



1975 



1985 



FIGURE 3.— Stainless steel ingot production by the United 
States, Japan, and the European Economic Community. 

importing ferrochromium and is now increasing its imports 
of stainless steels. Everyone at this conference knows what 
this means in terms of jobs, reduced salaries, mergers, plant 
closures, and even bankruptcy for some. Potential 
substitutes for Cr in stainless steels and other products will 
be discussed during this seminar, but we should be aware of 



98 



what is happening to one of our basic industries that has 
served this country well over the years. Good substitute 
materials are being developed, as we shall learn today and 
tomorrow, but let's not forget that we need the capacity to 
make them. 

The next speaker will be Mr. Gerald Smith of the 
Bureau's Avondale Research Center, who will talk about a 
technique for conserving Cr by electroplating a wide range 
of Fe-Ni-Cr alloy compositions. Thus, to conserve Cr, a com- 
plex shape can be cast or forged out of plain carbon steel, 
for example, and its surface protected against corrosion by 
electrodepositing a stainless-steel-type coating on all ex- 
posed surfaces. In a similar manner, strip material can be 
protected from corrosion by cladding. Cladding research 
was done here at the Albany Research Center, and if anyone 
is interested, a publication on this subject (14) is available. 

Casting research also is being done here. Following Mr. 
Smith's paper on coatings will be a presentation by Mr. Jef- 
frey Hansen on new casting techniques that conserve Cr in 



equipment used by the mining industry. Be sure to note the 
unique use of styrofoam patterns when Mr. Hansen 
describes this casting technique. 

After these two talks, the one on coatings and the one 
on castings, the behavior of new materials that could 
substitute for some of the high-Cr alloys being used today 
will be discussed. Dr. David Flinn of the Avondale Research 
Center will talk about new surfacing techniques such as 
laser glazing, sputtering, and nitriding. Dr. Flinn's interest 
is in understanding the basic surface properties of materials 
made by these techniques. He also will talk about conserving 
Cr during the many pickling operations that are used bet- 
ween passes when stainless steel is rolled into sheet or plate. 

Following Dr. Flinn's presentation, Dr. John Dunning 
will tell us about new alloys being developed at the Albany 
Research Center. Dr. Dunning's current interest is in the 
oxidation behavior of these materials, but he also will 
discuss sulfidation and aqueous corrosion. 



CONCLUSION 



All of these presentations represent more than just op- 
portunities for learning about techniques for conserving Cr. 
They also represent opportunities for an exchange of ideas. 
We in the Bureau of Mines hope that each one of you will 



take back with you at least one idea that will help our Na- 
tion's basic industries that depend on uninterrupted supplies 
of Cr, whether it be for chemicals, refractories, or metals 
and alloys. 



REFERENCES 



1. Papp, J. F. Chromium. Ch. in Minerals Yearbook 1983, v. 1, 
pp. 203-220. 

2. National Materials Advisory Board. Contingency Plans for 
Chromium Utilization. Natl. Acad. Sci., NMAB-355, 1978, 347 pp. 

3. Gordon, J. K. U. S. To Test, Certify Cobalt-Free Aircraft 
Alloys. Aviation Week and Space Technol., Jan. 28, 1985, p. 77. 

4. Curwick, L. R., W. A. Petersen, and H. V. Makar. Availabili- 
ty of Critical Scrap Metals Containing Chromium in the United 
States: Superalloys and Cast Heat- and Corrosion-Resistant alloys. 
BuMines IC 8821, 1980, 51 pp. 

5. Kusik, C. L., H. V. Makar, and M. R. Mounier. Avilability of 
Critical Scrap Metals Containing Chromium in the United States: 
Wrought Stainless Steels and Heat-Resisting Alloys. BuMines IC 
8822, 1980, 51 pp. 

6. Dunning, J. S., M. L. Glenn, and H. W. Leavenworth, Jr. 
Substitutes for Chromium in Stainless Steels. Met. Prog., Oct. 
1984, pp. 19-24. 

7. U.S. Bureau of Mines. Chromium. Mineral Commodity Sum- 
maries, 1985, 32 pp. 



8. Stalker, K. W., C. C. Clark, J. A. Ford, F. M. Richmond, and 
J. R. Stephens. An Index To Identify Strategic Metal Vulnerability. 
Met. Prog., Oct. 1984, pp 55-65. 

9. Thomas, P. R., and E. H. Boyle, Jr. Chromium Availability, 
Market Economy Countries. A Minerals Availability Program Ap- 
praisal. BuMines IC 8977, 1984, 86 pp. 

10. O'Shaughnessy, D. P., and C. M. Offenhauer. Developments 
in Chromium in 1982. J. Met., Apr. 1983, pp. 85-87. 

11. Zucherman, E. Pentagon in Key Chromium Ruling. Am. Met. 
Mark., v. 92, No. 21, Jan. 31, 1984, p. 1. 

12. Kramer, D. GSA Proposes 'Buy America' for Chromium. Am. 
Met. Mark., v. 93, No. 45, Mar. 7, 1985, p. 1. 

13. U.S. Congress, Office of Technology Assessment. Strategic 
Materials: Technologies To Reduce U.S. Import Vulnerability. Jan. 
1985, 56 pp. 

14. Blickensderfer, R. Cladding of Metals to Iron by Vacuum 
Rolling. BuMines RI 8481, 1980, 25 pp. 



BuMines IC 9087: Chromium-Chromite: Bureau of Mines Assessment and Research 



99 



CHROMIUM ALLOY COATINGS— A NEW METHOD OF PREPARATION 

By G. R. Smith, 1 J. E. Allison, Jr., 2 and W. J. Kolodrubetz 3 



ABSTRACT 



As part of a research program on conservation of criti- 
cal metals, a modified aqueous electrodeposition method for 
preparing stainless-steel-type alloy coatings has been 
studied. This method involved mechanically suspending Cr 
powder (av 2-/*m diam) in a ferrous-nickelous sulfate elec- 
troplating bath and occluding the Cr particles in the elec- 
trodeposited Fe-Ni alloy matrix. Subsequent heat treatment 
of the resulting composite coating formed the ternary alloy. 
The occlusion process was affected by the quantity of Cr 
powder suspended as well as by the microstructure and 
composition of the electrodeposited matrix. The largest 



quantity of Cr was occluded when the electrodeposited 
matrix exhibited a dual-phase 7(Ni,Fe)-a(Fe,Ni) microstruc- 
ture. Coatings with up to 21 pet Cr have been deposited 
from an electrolyte containing 20 vol pet suspended Cr 
powder. Heat treatment at 1,100° C for 8 h effectively 
homogenized the composite coating. A 55 Fe-29Ni-16Cr 
alloy produced by this method corroded at a rate of only 0.7 
mm/yr during 240 h of exposure to boiling 65-pct HN0 3 . Ap- 
plicability of this method to the preparation of electroforms 
has also been demonstrated. 



INTRODUCTION 



It has been known for many years that insoluble par- 
ticles present in a electrolyte during plating can be occluded 
in the electrodeposited metal. In recent years, occlusion has 
been used advantageously to produce electrodeposited com- 
posite coatings called cermets (1-12). These composites con- 
tain a variety of ceramic particles including oxides, nitrides, 
and carbides that serve to improve the oxidation or wear 
resistance of the electrodeposit. A possible extension of the 
use of the occlusion method is in the production of composite 
coatings containing metal particles. Subsequent heat treat- 
ment can yield alloy coatings, such as stainless steels, that 
would be very difficult to prepare by conventional aqueous 
electrolysis methods. Although two reports have suggested 
that the occlusion method could be used to produce stainless 
steel coatings (13-14), they did not give specific details of the 
method or evidence of its feasibility. Initital research results 
obtained by the Bureau of Mines (15) provided experimental 
evidence of the feasibility of this method. 

The present paper presents further results of ex- 
periments conducted to produce stainless-steel-type Fe-Ni- 
Cr alloy coatings using the particle occlusion heat-treatment 



1 Supervisory research chemist. 

2 Physical metallurgist. 

3 Chemist. 

Avondale Research Center, Bureau of Mines, 4900 LaSalle Rd., Avondale, 
MD 20782. 



method. It addresses the effects of current density, elec- 
trodeposit composition and microstructure, and concentra- 
tion of suspended Cr powder on the quantity of Cr particles 
occluded in the composite coatings, and includes a discus- 
sion of the heat treatment required to homogenize the com- 
posite coatings as well as an evaluation of the corrosion 
resistance exhibited by the resulting ternary alloy. 



Abbreviations Used in This Paper 


A/dm 2 


ampere per decimeter squared 


°C 


degree Celsius 


°C/h 


degree Celsius per hour 


dm 2 


decimeter squared 


h 


hour 


mm 


millimeter 


mm/yr 


millimeter per year 


/tm 


micrometer 


mol/L 


mole per liter 


mol pet 


mole percent 


pet 


weight percent 


rpm 


revolution per minute 


vol pet 


volume percent 



100 



EXPERIMENTAL WORK 



ELECTROLYTIC CELL 

A polymethylmethacrylate plating cell, 100 mm diam by 
135 mm high (fig. 1), was used to prepare the composite 
coatings. Two electrolytically pure Ni anodes and two 
99.6-pct-pure Fe anodes were placed opposite each other 
and positioned 30 mm from a cold-drawn AISI 1020 steel 
rod cathode. The diameter of the cathode was 10 mm, and 
the effective plating area was 0.13 dm 2 . The quantity of cur- 
rent passing through each set of anodes was controlled by 
two dc power supplies connected in parallel to the cell. This 
permitted accurate control of the dissolution and deposition 
rates. Total charge passed through the cell was measured 
using an ampere-hour meter. 

The composition of the electrolyte used in the prepara- 
tion of the composite coatings is listed in table 1. Although 
the total metal ion concentration was maintained at 1.78 
mol/L, the relative ratio of Fe 2 * and Ni 2 * in the electrolyte 
was varied in order to change the composition of Fe and Ni 
in the electrodeposit. Sodium saccharin was added to relieve 
internal stresses in the electrodeposit. 



TABLE 1.— Electrolyte composition 

Constituent Cone, mol/L 

Total metal ion (Fe 2 *, Ni J *) 1.78 

Sulfate ion 1.70 

Chloride ion .18 

Boric acid .65 

Sodium saccharin .04 



Chromium powder was suspended in the electrolyte by a 
motor-driven, 50-mm-diam, polypropylene propeller, posi- 
tioned near the base of the cell. A rotation speed of 360 rpm 
was employed in this study. 

Commercially available Cr powder (99.86 pet Cr) was 
used in the preparation of the composite coatings. The parti- 
cle size was ~ 2/tm (fig. 2) as determined by image analysis 
methods using the transmission electron microscope. The 
Cr particles have been observed to have a predominantly 
spherical shape. 

EVALUATION OF COMPOSITE COATINGS 

The composition of the composite coatings was deter- 
mined by dissolving the Fe-Ni alloy matrix in 10-pct HN0 3 
and recovering the insoluble Cr particles by filtration. 
Dissolution of the coating was carried out after mechanical 
removal from the cathode. The concentration of the dis- 
solved Ni was determined by atomic absorption. The Fe con- 
centration was calculated by difference. X-ray diffraction 
methods were used to elucidate the microstructure of the 
composites. Scanning electron microscopy (SEM) and 
energy-dispersive X-ray analysis (EDAX) were used to ex- 
amine the distribution characteristics of the Cr powder 
within the electrodeposited matrix. 

HEAT TREATMENT OF COMPOSITE COATINGS 




CO 



Dual dc 
power supply 



TOP VIEW 

Iron anode 
Nickel anode 



SIDE VIEW 

-Nickel anode 
■ Cathode 

- Iron anode 

- Plastic 
-Stir rod 



Heat treatment was carried out at 1,100° C in an Astro 
vacuum furnace, 4 model 1100 V, using a heating rate of 60° 
to 120° C/h. After heat treatment, the samples were al- 
lowed to cool in the furnace at a typical rate of ~ 1,000° C/h. 
Each sample was then reheated to 1,100° C under an N at- 
mosphere and quenched in water to prevent segregation of 
carbides and possible formation of sigma (a) phase. 

EVALUATION OF HEAT-TREATED COATINGS 

Two types of samples were prepared for post-heat- 
treatment evaluation of the Fe-Ni-Cr alloy coatings. The 
first type had been removed from the substrate prior to heat 
treatment. This provided a means for evaluating the alloy 
independent of any effects related to substrate-coating in- 
terdiffusion. Evaluation consisted of exposing the alloys to 
boiling 65-pct HN0 3 in five 48-h stages (Huey test for 
stainless steels). Comparison of the corrosion rates of 
coatings with different heat treatments was then made. In 
the second type of sample the coating and substrate remain- 
ed an integral unit during heat treatment. This type of sam- 
ple provided a means for determining the extent of 
substrate-coating interdiffusion during heat treatment and 
the corresponding capability of an Ni barrier coating to limit 
this interdiffusion. Prior to deposition of the Ni barrier 
coating from a standard Watts Ni electrolyte, the substrate 
was acid-cleaned in a 10-pct HN0 3 solution, then in a 25-pct 
HC1 solution, followed by a water rinse. 



FIGURE 1.— Schematic of electroplating assembly. 



4 Reference to specific products does not imply endorsement by the Bureau 
of Mines. 



101 




SIZE, M m 

FIGURE 2.— Particle-size distribution of Cr powder. 

RESULTS AND DISCUSSION 



PREPARATION OF COMPOSITE 
COATINGS 

Powder Suspension Effects 

To determine the effect of Cr powder concentration on 
the quantity of particles occluded, the Cr suspension was 
varied from 0.3 to 30 vol pet for a series of electrodeposits 
prepared at 2.5 A/dm 2 . The Cr was occluded into an 86Fe-14 
Ni electrodeposited alloy matrix using an electrolyte con- 
taining 60 mol pet Fe 2 * and 40 mol pet Ni 2 *. 

Figure 3 shows that the Cr content in the composite 
coatings increased significantly as the concentration of 
suspended Cr powder was increased above 1 or 2 vol pet. 
These data are consistent with a model proposed by and ex- 
perimentally confirmed by Guglielmi (12) for the occlusion of 
ceramic particles in an electrodeposited Ni matrix. The 
model was further confirmed by Celis and Roos (16) in their 
investigation of the occlusion of A1 2 3 in an electrodeposited 
Cu matrix. A schematic of this model is shown in figure 4. 
The model consists of a two-step mechanism in which loose- 
ly adsorbed particles on the cathode are in equilibrium with 
the positively charged suspended particles. The adsorbed 
particles are then irreversibly occluded into the elec- 
trodeposit. The mathematical expression for this model 
relates a Langmuir adsorption isotherm constant to the 



reversible adsorption step and the metal deposition 
parameters to the occlusion step. 

Matrix Composition and Microstructure Effects 

The quantity of Cr particles occluded varied significant- 
ly as the composition and microstructure of the matrix 
changed. Using a 20-vol-pct suspension to ensure a suffi- 
cient quantity of Cr particles, electrolysis results were ob- 
tained at current densities of 2, 5, and 10 A/dm 2 over the full 
range of matrix composition (fig. 5). These results showed 
that (1) the quantity of Cr particles occluded increased as 
the Fe in the -y(Ni-Fe) matrix increased and (2) the largest 
quantities of Cr particles were occluded when electrolysis 
conditions yielded a mixed -><Ni-Fe)-a(Fe-Ni) or an a(Fe-Ni) 
microstructure. This relationship between Cr particle occlu- 
sion and matrix composition and microstructure may be 
associated with the compatibility of the particle and matrix 
lattice structures. Specifically, both Cr and a(Fe-Ni) exhibit 
a body-centered cubic lattice structure, whereas y(Ni-Fe) 
exhibits a face-centered cubic lattice structure. The quantity 
of Cr particles occluded in an electrodeposited matrix com- 
posed only of a-Fe was 12 times higher than that in a matrix 
containing only 7-Ni. In general, the quantity of chromium 
occluded at any matrix composition increased as the current 
density was increased. 



102 




5 10 15 20 

Cr POWDER, vol pet 

FIGURE 3.— Relationship between Cr powder suspended and occluded. 



25 



30 




Ionic adsorption 
on particles 



Reversible adsorption 
on cathode 



Occlusion in 

electrodeposited 

alloy 



Fe-Ni matrix 



FIGURE 4.— Schematic model of occlusion process. 



103 



24 



KEY 
■ 10 A/dm 2 
• 5 A/dm 2 
A 2 A/dm 2 




40 60 

Fe, wt pet 

FIGURE 5.— Effects of Fe-Ni matrix composition and microstructure on occlusion of Cr. 



100 



HEAT TREATMENT OF COMPOSITE COATINGS 

The extent of coating homogenization was determined 
for heat-treated coatings containing 78Fe-10Ni-12Cr. Cross 
sections of these coatings before and after heat treatment at 
1,100° C for 1 h are shown in figure 6. The SEM photo of 
the unhomogenized composite shows discrete Cr particles 
distributed uniformly throughout the Fe-Ni alloy matrix. An 
EDAX map at the same location shows the occluded Cr ap- 
pearing as bright areas. After heat treatment, significant 
Cr diffusion was evident. Individual 2-^m particles could not 
be distinguished in the matrix. The corresponding EDAX 
map substantiates this result. During heat treatment of 
these samples, some interdiffusion of the coating and the 
1020 AISI steel substrate occurred. The relative intensities 
of Cr and Ni near the coating-substrate interface, as deter- 
mined by EDAX, showed that a coating 125 ^m thick ex- 
hibits a diffusion zone - 80 ^m wide after heat treatment. 

An important factor that had to be considered in 
evaluating the effects of coating-substrate interdiffusion 
was the control of the quantity of carbon migrating from the 
substrate to the coating. In the presence of > 0.02 pet C, the 
chromium carbide (Cr 3 C 2 ) phase is likely to precipitate at 
the Fe-Ni-Cr alloy grain boundaries (sensitization). This is 
detrimental to the corrosion resistance of the alloy because 
of accelerated attack at the grain boundaries. A 50-/im-thick 
electrodeposited Ni undercoat effectively decreased the dif- 
fusion of carbon from substrate to coating during heat treat- 
ment at 1,100° C for 1 h. Micrographic examination of the 
Ni-substrate interface (fig. 7) showed a significant concen- 
tration of carbides (right photo, dark areas) associated with 
carbon that had been blocked from entering the coating. 



Without the Ni undercoat (left photo), the region of the 1020 
steel substrate adjacent to the coating was decreased from 
the normal 0.2 pet C in this steel to <0.02 pet C, and car- 
bides were evident in the coating. On the basis of these 
results, the possibility of preparing a protective Fe-Ni-Cr 
alloy coating on an inexpensive substrate appears promis- 
ing. 

To effectively determine the heat-treatment conditions 
required to homogenize the Fe-Ni-Cr powder composites, 
that is, produce a corrosion-resistant alloy, the coatings 
were mechanically removed from the substrate prior to heat 
treatment. This made possible an evaluation of the heat- 
treatment process independent of effects related to 
substrate-coating interdiffusion or coating porosity. Subse- 
quent corrosion rate data then served to establish the effec- 
tiveness of the heat-treatment procedure. 

Effect of Heat-Treatment Pressure on Corrosion 
Rate 

The corrosion rate data for composite coatings heat- 
treated at three pressures are shown in table 2. Each of 
these 250-/tm-thick composites contained ~ 55 pet Fe, 29 pet 
Ni, and 16 pet Cr and was heat-treated for 8 h at 1,100° C. 



TABLE 2.— Effect of pressure during heat treatment 
(8 h, 1,100°C) upon corrosion rate of a 55Fe-29Ni-16Cr alloy 

Corrosion 
Pressure, ton rate, mm/yr 

1 x 10-* 1.3 

1 x 10"* .9 

1 x10° .7 



104 



■ 


#" ' 








**!»■*•* w lit 


': *> '^J^ 1 '* V fas' - ' ^ " ; 


^* 


,-||f 5 


Scale, fin J 




Composite coating 



EDAX of composite coating 




Heat-treated coating EDAX of heat-treated coating 

FIGURE 6.— Photomicrographs and EDAX (for Cr) before and after heat treatment. 



"V, 







Carbide 






iaJi***^ 



' 



fr&m* 



:% 



» Fe-Ni-Cr coating. 



^?X/<^*^T, 




^ ; ^*^ 



:^\- ^A^ 



Ni undercoat 



Fe-Ni-Cr coating 



100 

_j 



Scale, jjm 



FIGURE 7.— Effect of an Ni undercoat on carbon diffusion from the carbon-steel substrate into the Fe-Ni-Cr alloy coating. A, 
Carbide-free zone near the substrate-coating interface associated with carbon diffusion into the coating; 6, use of an Ni under- 
coat retards this diffusion. 



105 



The composite heat-treated at 1 Torr exhibited the lowest 
corrosion rate during 240 h of exposure to boiling 65 pet 
HN0 3 . A comparison with the corrosion rate of a commer- 
cial 304 stainless steel shows that, in this corrosive environ- 
ment, the Fe-Ni-Cr alloy was approaching the 0.2-mm/yr 
corrosion rate of the stainless steel. 

Effect of Heat-Treatment Time on Corrosion Rate 

The improved corrosion resistance at the highest 
pressure is consistent with other results showing better cor- 
rosion resistance when the heat-treatment time was 
decreased from 16 h to 8 h using 1 x 10~ 6 Torr pressure 
(table 3). There is assumed to be an excessive loss of Cr 
through sublimation at the lower pressures and the longer 
heat-treatment times. When only 4 h of heat treatment was 
employed, the higher corrosion rates were indicative of in- 
complete homogenization. 

TABLE 3.— Effect of duration of heat treatment (1,100° C, 1 x 
10" Torr) upon corrosion rate of a 55Fe-29Ni-16Cr alloy 

Corrosion 
Heat treatment, h rate, mm/yr 

4 3.7 

8 1.3 

16 2.5 



ELECTROFORMING 

Practical application of the alloy coating method for the 
preparation of small electroforms has been demonstrated. 



Figure 8 shows three examples of these electroforms, 
prepared at 5 A/dm 2 in an electrolyte having a 3:1 Ni 2 *-Fe 2 * 
ratio and containing 20 vol pet suspended Cr powder. The 
electroformed cylinder (right) was prepared by elec- 
trodepositing the Fe-Ni-Cr powder composite on a 1020 
steel rod, heat-treating at 1,100° C for 4 h, and subsequent- 
ly dissolving the rod (mandrel) with HN0 3 . The other two 
electroforms were prepared using a more practical mandrel 
material. A polyethylene wax mandrel plated with a thin 
electroless Ni coating and a 25-jim-thick electrodeposited Ni 
coating served as the base upon which an Fe-Ni-Cr elec- 
troform, 750 /tm thick, was deposited. After deposition the 
form was removed from the mandrel by heating the wax to 
its melting point of 110° C. A cylindrical, 12-mm-diam, 
38-mm-high beaker (left) and a rectangular container, 12 
mm square and 32 mm high, with a round base (center) thus 
resulted. Each of the electroforms was then heat-treated at 
1,100° C for 8 h to homogenize the composite into a ternary 
alloy. A uniform composition was achieved throughout the 
rectangular form as indicated by the analytical results 
shown in table 4. Chromium and nickel values were obtained 
by X-ray techniques. Corresponding values for Fe were 
determined by difference. 



TABLE 4.— Composition of rectangular electroform, percent 


Side 


Fe 


Ni 


Cr 


1 

2 

3 

4 


45.7 
45.2 
44.0 

44.6 


34.3 
34.6 
36.9 
35.2 


20.0 
20.2 
19.1 
20.2 




Scale, mm 



FIGURE 8.— Fe-Ni-Cr alloy electroforms. 



106 



CONCLUSIONS 



Coatings of Fe-Ni-Cr alloy up to 750 Jim thick have been 
prepared by a method employing occlusion of Cr particles in 
an electrodeposited Fe-Ni alloy. A uniform Cr distribution 
has been achieved, and a wide range of alloy compositions 
can be produced. Heat treatment at 1,100° C homogenizes 
the Fe-Ni-Cr alloy, and an Ni precoat effectively decreases 
the quantity of detrimental carbon diffusing from the 1020 
steel substrate to the coating during heat treatment. Corro- 



sion rates as low as 0.7mm/yr have been observed for the 
alloy when exposed to boiling 65-pct HN0 3 . Under similar 
conditions, a commercial 304 stainless steel corrodes at 0.2 
mm/yr. Possible application of the coatings process to the 
preparation of small electroforms has been shown, and the 
ability to prepare a protective Fe-Ni-Cr alloy coating on an 
inexpensive carbon steel substrate appears promising. 



REFERENCES 



1. Foster, J., and B. Cameron. The Effect of Current Density and 
Agitation on the Formation of Electrodeposited Coating. Trans. In- 
st. Met. Finish., v. 54, 1976, pp. 178-182. 

2. Grazen, A. E. Plating Process Co-Deposits Oxides or Carbides. 
Iron Age, v. 183, No. 5, 1959, pp. 94-96. 

3. Kariapper, A. M. J., and J. Foster. Further Studies on the 
Mechanism of Formation of Electrodeposited Composite Coatings. 
Trans. Inst. Met. Finish., v. 52, 1974, pp. 87-91. 

4. Pushpavanam, N., G. Vardajan, S. Krishnamurthy, and B. A. 
Shenoi. Electrodeposited Composite Coatings. Electroplat. and 
Met. Finish., v. 27, No. 5, 1974, pp. 10-15. 

5. Snaith, D. W., and P. D. Groves. A Study of the Mechanisms of 
Cermet Electrodeposition. Trans. Inst. Met. Finish., v. 50, No. 3, 
1972, pp. 95-101. 

6. Some Further Studies of the Mechanism of Cermet 

Electrodeposition: Part 2 - Variable Factors in the Process of Elec 
trodeposition of Metal-Matrix Composites. Trans. Inst. Met. 
Finish., v. 56, 1978, pp. 8-14. 

7. Tomaszewski, T. W. Effects of Anions on the Formation of 
Electrodeposited Composite Coatings: Some Experimental 
Evidence. Trans. Inst. Met. Finish., v. 54, 1976, pp. 44-48. 

8. Tomaszewski, T. W., R. J. Clauss, and'H. Brown. Satin Nickel 
by Co-Deposition of Finely Dispersed Solids., Paper in Technical 
Proceedings of the 50th Annual Convention of the American Elec- 
troplates' Society (Atlantic City, NJ, June 23-27, 1963). Am.Elec- 
troplat. Soc., Newark, NJ, 1963, pp. 169-202. 



9. Tomaszewski, T. W., L. C. Tomaszewski, and H. Brown. 
Codesposition of Finely Dispersed Particles With Metals. Plating, 
Nov. 1969, pp. 1234-1239. 

10. Withers, J. C. Electrodepositing Cermets. Prod. Finish. (Cin- 
cinnati), v. 26, No. 11, 1962, pp. 62-68. 

11. Zahavi, J. and H. Kerbel. Properties of Electrodeposited 
Composite Coatings as a Result of Their Formation Conditions. 
Paper D-3 in General Session (Technical Proceedings of the 68th 
Annual Technical Conference of the American Electroplaters' 
Society, Boston, MA, June 28-July 2, 1981). Am. Electroplat. Soc, 
Winter Park, FL, 1981, 43 pp. 

12. Guglielmi, N. Kinetics of the Deposition of Inert Particles 
From Electrolytic Baths. J. Electrochem. Soc, v. 119, No. 8, 1972, 
pp. 1009-1012. 

13. Kilgore, C. R. Engineered Composite Coatings. Prod. Finish. 
(Cincinnati), v. 27, No. 8, 1963, pp. 34-40. 

14. Williams, R. V. Electrodeposited Composite Coatings. Elec- 
troplat. and Met. Finish., v. 19, No. 3, 1966, pp. 92-96. 

15. Allison, J. E., Jr., and G. R. Smith. Alloy Plating Using a Par- 
ticle Occlusion Method. Paper K-2 in Alloy Plating I (Technical Pro- 
ceedings of the 71st Annual Technical Conference of the American 
Electroplaters' Society, New York, July 16-19, 1984). Am. Elec- 
troplat. Soc, Winter Park, FL, 1984, 14 pp. 

16. Celis, J. P., and J. R. Roos. Kinetics of Alumina Particles 
From Copper Sulfate Plating Baths. J. Electrochem. Soc, v. 124, 
No. 10, pp. 1508-1517. 



BuMines IC 9087: Chromium-Chromite: Bureau of Mines Assessment and Research 



107 



WEAR PROTECTION OF IRON-BASE CASTINGS 
BY CAST-ON HARD SURFACING 

By Jeffrey S. Hansen 1 



ABSTRACT 



To reduce wear and maintain toughness in Fe-base 
castings, the Bureau of Mines has investigated a process to 
bond hard surfacings to cast parts while the part is being 
cast. Wear-resistant material in powdered form is applied 
on a polystyrene pattern, the pattern is embedded in a mold 
of unbonded sand, and the wear-resistant material is 
transferred to a casting surface at the time of pouring. The 
process eliminates the labor involved in applying conven- 
tional hard surfacings, reduces the danger of surfacing 



warpage and heat cracking, allows concurrent heat treat- 
ment of the part and hard surfacing, and produces a 
metallurgical bond between the hard surfacing and casting. 
In field tests, bucket-wheel excavator teeth and plowshares 
with cast-on hard surfacings had wear lives that were equal 
to or longer than those of similar parts with conventional 
hard facings. Surfacings composed of chromium white 
irons, tungsten carbide (WC), and WC with titanium carbide 
(TiC) have been applied successfully. 



INTRODUCTION 



The Bureau of Mines is investigating methods to reduce 
the need for imported metals, such as Mn, Cr, and Ni, in Fe- 
base alloys in order to minimize the Nation's dependency on 
foreign sources of these critical materials. Applications of 
hard surfaces to areas of cast parts that are subject to wear 
is an effective means of conserving wear-reducing alloying 
metals because the necessity for alloying the entire casting 
is eliminated. Surfacing operations also are effective 
because the enhancement of wear resistance is not ac- 
complished at the expense of toughness. These two proper- 
ties are mutually desirable in many applications, and par- 
ticularly in mining and metallurgical processing equipment. 

Commercially, hard surfacings have been applied to a 
variety of parts by weld overlaying and by flame and 
detonation-gun spraying. However, greater usage of such 
methods has been impeded by a number of difficulties. Weld 
overlaying can be prohibitively expensive; the heat 
generated during welding can cause distortion or cracking 
and loss of heat-treated properties, and weld overlays are 
sometimes brittle and susceptible to shock. Flame and 



detonation-gun hard surfacings suffer from these same 
faults and, in addition, generally have weak bonds and less 
than theoretical density. 

The Bureau has investigated a new method for applying 
hard surfacings. The method, called cast-on surfacing, 
eliminates most of the drawbacks that arise from other sur- 
facing methods. Hard surfaces applied by the cast-on proc- 
ess are thick, heat-treatable, and metallurgically bonded. 
When compared with conventional surfacing processes, 
cast-on surfacing eliminates several steps and greatly 
reduces the dangers of warpage and heat cracking. 



1 Group supervisor, Albany Research Center, Bureau of Mines, P.O. Box 
70, Albany, OR 97321. 



J 


Abbreviations Used in This Paper 


DPH 

h 


diamond pyramid hardness 
hour 


in 


inch 


lb 

mg/m 

mm 3 


pound 

milligram per meter 

cubic millimeter 


pet 


weight percent 



108 



BACKGROUND 



Cast-on surfacing is a method whereby powdered, wear- 
resistant material that has been applied to a polystyrene 
pattern is transferred and fused, with the assistance of 
vacuum, to the surface of a casting during pouring. The con- 
cept of cast-on surfacing as developed by the Bureau is a 
unique combination of two technologies, neither of which is 
new. 

The first technology, that of transferring a dissimilar 
metal to a casting during pouring, dates back to 1913 (1). 
Since then, a variety of techniques have been tried to ac- 
complish the same result. Liquid metals have been cen- 
trifugally cast against other liquids (2) and also against 
solids that have been heated to a point sufficient to promote 
fusion {8-4). These techniques generally are limited to simple 
geometries and narrow composition limits. 

Other researchers have attempted to cast metals into 
molds containing sintered powder compacts that are at- 
tached to mold walls (5-7). Most recently, loose powders 



have been pasted in molds or held in place by vacuum (8-9). 
Generally, however, consistency and predictability have not 
been achieved. In addition, most researchers have en- 
countered problems with erosion, shrink voids, excessive 
dilution, poor infiltration, uneven thickness, poor surface 
finish, and porosity. 

The second technology used in the Bureau cast-on sur- 
facing process involves a novel casting process in which an 
expendable polystyrene pattern is consumed during each 
cast (10-11). The pattern, which is embedded in a flask of un- 
bonded sand, is vaporized as it is replaced by liquid metal. 
As with previous attempts to cast-on surfacings, the 
polystyrene pattern casting technique has not been univer- 
sally accepted. However, new advances are continually be- 
ing made, and one market research firm predicts that by 
1995, polystyrene pattern casting will account for 15 pet of 
total ferrous casting tonnage (12). 



THE PROCESS OF CAST-ON SURFACING 



Initially, the polystyrene pattern technique was thought 
to be the best way to avoid the difficulties that had plagued 
earlier researchers of cast-on surfacing. Foremost among 
its advantages is that a pattern can be oriented in a sand 
mold in any one of several positions. Because of this posi- 
tioning flexibility, an orientation can be selected that is least 
likely to disturb powdered surfacing material during pour- 
ing. In addition, lightweight polystyrene patterns can be 
coated with powdered surfacing materials, thoroughly 
dried, and stored until needed. 



Use of vacuum was seen as necessary to draw off gases 
generated by vaporizing the pattern and to assist in drawing 
the molten casting metal into the powdered surfacing. It 
seemed a relatively simple task to combine the use of 
vacuum with existing polystyrene pattern technology. As 
the research progressed, this assumption was proved valid. 

Figure 1 shows the Bureau's polystyrene pattern cast- 
on surfacing process. The first step entails making a pattern 
from polystyrene either by molding pre-expanded beads or 
by cutting and machining parts from a solid polystyrene 




y ] ) 



^C I 




A polystyrene pat- 
tern is made- 



Gates and risers are 
attached. 



Powdered hard material paste 
is applied to wear-prone 
surfaces. 




Sand is vibrated around the pattern 
in a hollow-walled flask. 



The flask is sealed with plastic 
and evacuated. Upon pouring, the 
pattern vaporizes, and the hard 
material is fused to the casting. 



A refractory coating is sprayed 
on the entire pattern. 




The 
the 



vacuum is released and 
casting drops away. 



FIGURE 1.— Process steps for applying cast-on surfacings to polystyrene pattern castings. 



109 



block. To minimize gassing, the polystyrene density must be 
lower than the density of similar polystyrene that-is used to 
make household items. Sprues and gates to direct metal to 
the pattern are attached. Risers must also be attached to 
provide a source of liquid metal to the solidifying casting 
and prevent shrinkage. Joints must be filled if necessary, 
and appropriate fillets used in corners. 

The next step involves the placement of the surfacing 
material in powdered form onto the pattern. Surfacing 
materials that have been applied successfully include fer- 
rochrome, white iron compositions, tungsten carbide (WC), 
and mixtures of WC and titanium carbide (TiC). Two ap- 
plication methods have been used. With one method, the 
surfacing powder with a binder and carrier is trowled on 
patterns in thicknesses up to x k in. In the second method, 
the binder and carrier are sprayed onto the pattern, and the 
pattern is dusted with the surfacing powder. The excess 
powder is shaken off, and additional layers are similarly ap- 
plied until the desired thickness is obtained. Once applied, 
the surfacing powder is thoroughly dried to drive off the 
carrier and to form an adherent layer. Figure 2 shows a rip- 
per tooth pattern with hard-surfacing material applied to a 
wear-prone surface. 

After the surfacing powders are placed and dried, the 
entire pattern, including the gating system, is sprayed with 
a commercially available refractory coating containing zir- 



con in alcohol. The refractory coating provides an effective 
barrier to interference from the molding sand that is subse- 
quently added. The refractory barrier also is needed to pre- 
vent burn-on defects and localized, massive sand drop. Like 
the hard surfacing, the refractory is thoroughly dried to pre- 
vent gassing when the part is cast. 

Next, the pattern is placed in a vacuum flask that has 
double walls (fig. 3). The inside walls are screened to allow 
the passage of pattern gas into the space between the walls. 
The outside walls are welded steel. Unbonded sand is filled 
in around the pattern to the flask top. 

With the sand and pattern in place, the flask is vibrated 
to increase the bulk density of the sand and fill all cavities. 
The flask is covered with a sheet of 0.003-in polyethylene. 
The assembly can be easily stored or transported. Prior to 
and during pouring, vacuum is applied to the flask to draw 
off gases, aiding contact of the metal with the powdered 
surfacing material and maintaining the mold shape. 

Steel coastings are poured at conventional pouring 
temperatures. The heat from the metal at these 
temperatures is sufficient to either melt the surfacing, as in 
the case of white iron powders, or allow the casting metal to 
infiltrate around the powder grains. Sand that adheres to 
the casting and does not pop off upon cooling to room tem- 
pature can be removed by shot-blasting or other conven- 
tional procedures. 




FIGURE 2.— Hard-surfacing material powder applied to the 
tip of a ripper tooth pattern. 



FIGURE 3.— Ripper tooth (without refractory coating) placed 
in unbonded sand in a double-walled vacuum flask. 



110 



LABORATORY TESTING AND EVALUATION 



Several experiences and studies reported in the 
literature showed that a system combining cast-on surfacing 
techniques with polystyrene pattern casting methods would 
contain many variables. Consequently, statistically designed 
2- and 3-level factorial experiments were used to evaluate 17 
individual and combined effects of several variables. The 
following is a list of the most important variables: 

Independent Variables Dependent Variables 



Binder type 
Binder level 
Surfacing particle size 
Surfacing thickness 
Casting thickness 
Pouring temperature 
Vacuum level 
Powder application 
technique 



Surfacing porosity 
Casting porosity 
Internal porsity 
Surfacing roughness 
Surfacing contour 
Proportion of unmelted 

surfacing 
Proportion of dendrites 

in surfacing 
Proportion of carbides 

in surfacing 
Wear resistance 



A casting was designed that allowed three separate 
samples to be cast simultaneously (fig. 4). After casting, 
each defect type on each sample was given a ranking from 1 
to 5 by three independent observers. The rankings were 
averaged to provide a numerical assessment of the defect 
severity. The averaged rankings of the defects and other 
variables were compared with independent variables by 
computer analysis. Surprisingly, good surfacings generally 
were obtained under a wide variety of conditions. 

One variable that deserves special mention because it in- 
fluenced surfacing quality most was surfacing thickness. 
Especially in ferrochrome and white-iron-based surfacings, 
thickness dictated the microstructure, which in turn deter- 
mined wear resistance. At a 1/16-in thickness, white iron 
surfacings were diluted substantially by steel from the 
casting, which resulted in a microstructure with few car- 
bides (fig. 5A). At a thickness of 3/16 in, the dendritic struc- 
ture disappeared entirely, and a substantial increase in car- 
bides was obtained (fig. 5B). Because these carbides have a 
microhardness of about 1,600 DPH, wear protection is af- 
forded against siliceous minerals, for example, which have a 
hardness of about 800 to 900 DPH. 

In addition to microstructural analysis, most surfacings 
were subjected to one or both of two types of wear tests. 
The first test simulates so-called low-stress abrasion in 
which the abrasive particle does not break down. A 1- by 
3-in sample is pressed against a rotating rubber-tired wheel 
while a measured amount of silica sand is dropped between 
the two. The action produces a wear scar in the sample. The 
scar is measured and compared with the wear scars of stan- 
dards and other materials. The test conforms to ASTM 
Standard G65-81 (13). 

The second test uses a rotating drum that is covered 
with garnet sandpaper. A weighted pin of the surfaced 



material is pressed against the drum as it rotates. The 
stress is considerably higher and sufficient to break the 
abrasive grains. The wear is measured similarly to the wear 
of dry-sand test specimens. There is no standard for the 
test. 

The results show that excellent wear resistance can be 
obtained with cast-on surfaces. Based upon the results ob- 
tained from commerical weld-rod hard facings, values of 11 
mm 3 for the dry-sand test and 3.0 mg/m for the pin-on-drum 
test have been arbitrarily selected as benchmarks. The first 
two entries in table 1 indicate the increase in wear 
resistance that is obtained by increasing surfacing thick- 
ness. In the case of commercial ferrochrome, the volume 
loss sustained by a 3/16-in-thick specimen was 8.3 mm 3 in 
the dry-sand test; this is about one-third the volume loss of 
21.6 mm 3 sustained by a similar specimen that was only 1/16 
in thick. Specimens with values lower than these numbers 
are considered very good. The table also shows test results 
for a custom-made 9-pct-C ferrochrome, two white irons, 
and a WC-TiC mix. For comparison, the results for a com- 
monly used WC-containing, commercial hard-facing alloy 
are shown at the bottom of table 1. 



TABLE 1.— Dry-sand rubber-wheel and pin-on-drum abrasion test 
results on cast-on surfacings 



Surfacing material 


Dry-sand test 
vol loss, mm 3 


Pin-on-drum test 
wt loss, mg/m 


Commercial FeCr (1/16-in) 

Commercial FeCr (3/16-ln) 

No. 2 custom FeCr (9 pet C) 

5C-21Cr-8.5Cb-9Mo white iron ... 
9C-22Cr-2Mo-1 Ni white Iron 
83WC-17TIC 


21.6 
8.3 
8.4 
11.7 
10.4 
9.3 
12.0 
13.2 
11.3 


Not tested 
1.68 

.87 
3.14 
2.51 

.15 


FeMo plus carbon 

NIHard IV (solid) 


2.54 
.40 


Weld-applied WC hard facing . . . 


.15 




FIGURE 4.— Three-sample pattern with powdered surfac- 
ings for determining the effect of variables upon defect occur- 
rence. 



Ill 




B 



I 






fL- 



FIGURE 5.— Microstructure of (A) 1/16-in-thick and (B) 3/16-in-thick white iron surfacings (X 200). 



While the wear tests are valuable for screening pur- 
poses, they often do not correlate with real-life conditions. 
It is important, therefore, to test materials under field con- 
ditions before judging their worth. Cast-on surfaces have 
been subjected to two field environments. 

The first field trial was accomplished on a bucket- wheel 
excavator (fig. 6) that is used to remove claylike overburden 
at a coal mine. Without surfacing protection, the teeth on 
the buckets wear out in about four 8-h shifts. With weld-rod 
hard surfacing, the teeth may last 48 shifts. 

The entire outside surfaces of two teeth were cast-on- 
surfaced with the 9-pct-C custom ferrochrome and the 
5C-21Cr-8.5Cb-9Mo white iron alloy seen in table 1. The 
teeth were run for 31 shifts on separate buckets but at iden- 
tical corner positions on the buckets. The mine supplied two 
weld-rod, hard-surfaced control teeth that were run for 
comparison. The wear of each tooth was assessed by noting 
the loss in length (fig. 7). The white-iron-surfaced tooth lost 
1/2 in. In comparison, the control teeth lost 1V4 in and IV2 in. 
In terms of length then, the white-iron, cast-on-surfaced 
tooth registered a 60-pct improvement over the best control 
tooth. The 9-pct-C ferrochrome-surfaced tooth was not as 
good. Since the test, porosity has been reduced, and the 
wear resistance of surfacings has been improved. Additional 
tests are planned to obtain statistical significance. 

In the second field trial, plowshares were cast-on- 
surfaced along the share wear edges and used to plow about 
140 acres of sandy, abrasive river bottom soil. Although 
plowshares normally are made of wrought steel and most 
likely will never be cast, the abrasion that occurs in plowing 
is similar to the abrasion that occurs in many other en- 
vironments. The sandy soil at the test farm caused unsur- 



faced blades to wear out after 25 acres or less. Weld-rod 
hard surfacing allowed the farmer to plow over 150 acres 
without replacing the plowshares. 

Plowshares are affixed to the bottoms of each of five 
blade assemblies similar to the one shown in figure 8. The 
shares make the initial contact with the soil and protect the 
remainder of the blade. Two field trials were conducted. The 
shares were located at several positions on the plow, as 
noted in table 2, because the outside shares (positions 1 and 
5) are subject to greater abrasion and typically wear more. 
As table 2 shows, the cast-on-surfaced shares performed ad- 
mirably. The ferrochrome and WC cast-on-surfaced shares 
lost about the same weight as equally placed weld-rod- 
surfaced shares. However, the 5C-21Cr-8.5Cb-9Mo white 
iron alloy that perfomed best in the bucket-wheel excavator 
test did somewhat worse than the weld-rod-surfaced shares. 
Figure 9 shows two shares after the field tests. In addition 
to showing good wearability, the tests demonstrated that 
cast-on surfaces can be successfully applied to thin section 
castings. 

TABLE 2.— Plowshare field trial results 



Surfacing material 


Plow position' 


Wt loss, lb 


Commercial ferrochrome 

5C-21Cr-8.5Cb-9Mo white Iron ... 

WC 

Weld-applied hard surfacing 


5 
4 
5 
4 
3 
1 
3 


1.0 

1.0 

1.3 

.8 

.7 

1.0 

.8 



'Plowshares numbered 1 and 5 are located in outside positions; 2 
through 4 are located in inside positions. 



112 




FIGURE 6.— One of eight buckets belonging to a bucket-wheel excavator at a coal mine. Nine teeth are fitted on the edge. 



£— • r 






FIGURE 7.— Bucket-wheel excavator teeth after return from field trials. Left, weld-rod hard-surfaced control tooth; middle, Fe- 
5C-21Cr-8.5Cb-9Mo composition white iron alloy cast-on-surfaced tooth; right, custom-melted ferrochrome cast-on-surfaced tooth. 



113 




FIGURE 8.— Plowshares affixed to the lower portion of plow blade assemblies. 




FIGURE 9.— Weld-rod hard-surfaced control plowshare (upper) and ferrochrome cast-on-surfaced plowshare (lower) after field 
trials. 



114 



CONCLUSIONS 



Cast-on surfacing using polystyrene patterns has the 
potential to become a viable surfacing technique. It 
eliminates the harmful localized heating that is associated 
with other surfacing processes and forms a composite struc- 
ture that will safely respond to heat treatment to develop 
good surface and casting properties. Strong metallurgical 
bonds are formed between the hard surfacing and casting, 
thereby increasing impact resistance and widening the field 
of surfacing applications. Wear resistance is substantially 
improved, and more importantly, critical materials are con- 
served. 



The polystyrene pattern casting technique is ideally 
suited to cast-on surfacing. Because parting surfaces can be 
ignored, patterns can be optimally oriented within a 
molding flask with respect to the surfaces intended for hard 
material application? Patterns can be prepared well in ad- 
vance of use and can be stored without tying up flasks and 
vacuum equipment for long periods prior to pouring. 

The potential of cast-on surfacings to replace weld-rod 
hard facings has been demonstrated in field tests on bucket- 
wheel excavator teeth and plowshares. Currently, other ap- 
plications are being sought, and additional field tests are 
underway to statistically strengthen the results. 



REFERENCES 



1. Morris, A. D. Method of Making Resistant Surfaces. U.S. Pat. 
1,072,026, Sept. 2, 1913. 

2. Page, M. L. Vertical Centrifugal Casting Raises Bi-Metal Roll 
Life. Met. and Mater., Feb. 1975, pp. 47-48. 

3. Kura, J. G. Cast Bonding Produces Quality Metallic Com- 
posites. Mater. Eng., v. 80, No. 5, Oct. 1974, pp. 60-61. 

4. Panhard, J. L. Methods of Manufacturing Crank-Case 
Envelopes for Rotary Piston Inernal Combustion Engines With 
Sintered Metal Plug Support. U.S. Pat. 3,744,547, July 10, 1973. 

5. Jackson, W. J., D. M. Southall, and D. S. Edwards. Surface 
Alloying of Steel Castings. Paper 17 in Advances in Surface 
Coating Technology. The Welding Inst., London, 1978, pp. 
201-218. 

6. Davis, K. G., and J. G. Magny. The Production of Castings 
With Abrasion-Resistant Coatings. Part I: Castings With Powder 
Compacts Set Into the Walls of Sand Moulds. CANMET Rep. 
MRP/PMRL 78-4, Oct. 1978, 40 pp. 



7. Mikhailov, A. M. Surface Hardening of Castings With Alloying 
Materials. Russ. Cast. Prod., 1970, pp. 82-84. 

8. Steel Castings Research and Trade Association (Sheffield, 
England). Improvements in or Relating to Casting. Republic of 
South Africa Pat. 773027, May 20, 1977. 

9. Davis, K. G., and J. G. Magny. Cast-In-Place Hard Surfacing. 
CANMET Rep. MRP/PMRL 80-68, Sept. 1980, 56 pp. 

10. Shroyer, H. F. Cavityless Casting Mold and Method of Mak- 
ing Same. U.S. Pat. 2,830,343, Apr. 15, 1958. 

11. Smith, T. R. Method of Casting. U.S. Pat. 3,157,924, Nov. 24, 
1964. 

12. Foundry Management and Technology. Foundry Markets. V. 
12, No. 11, Nov. 1984, p. 9. 

13. American Society for Testing and Materials. Standard Prac- 
tice for Conducting Dry Sand/Rubber Wheel Abrasion Tests. 
G65-81 in 1981 Annual Book of ASTM Standards: Part 10, 
Metals -Physical, Mechanical, Corrosion Testing. Philadelphia, 
PA, 1981, pp. 1044-1061. 



BuMines IC 9087: Chromium-Chromite: Bureau of Mines Assessment and Research 



115 



OPTIMIZATION OF MATERIALS SELECTION 
THROUGH CORROSION SCIENCE 

By D. R. Flinn 1 



ABSTRACT 



The cost of corrosion to the U.S. economy is very large. 
It includes accelerated maintenance or replacement or other 
mitigation methods, as well as the importation of critical 
metals, including Cr, for use in alloys that have been shown 
to be resistant to corrosion in many environments. Reduc- 
tion of these costs depends on an improved fundamental 



understanding of corrosion processes as well as wide 
dissemination of this information. The approach of the 
Bureau of Mines to understanding corrosion phenomena 
through both fundamental and applied studies is discussed, 
and examples of the techniques used and results attained 
are given. 



INTRODUCTION 



The cost of metallic corrosion to the U.S. economy was 
estimated to be $70 billion in 1975 (1). This figure 
represented 4.2 pet of the gross national product for that 
year, a figure that agrees well with studies from other coun- 
tries. In the same study (1), it was estimated that $10 billion 
of this cost could have been avoided by use of currently 
available technology. Logically, decisions should be made to 
implement corrosion control procedures when the 
economics are favorable or where health and safety factors 
are involved. Unfortunately, even when these conditions ex- 
ist, there may be insufficient knowledge about material per- 
formance in a given environment to make cost-effective 
choices; or, in some cases, no commercially available 
material may be able to provide the required service life. 

For many years the Bureau of Mines has conducted 
research to expand the information base on corrosion prop- 
erties of new materials and to determine cost-effective 
materials for use in mineral and material processing en- 
vironments. In the early 1930's, Bureau scientists at what 
was then the Bureau of Mines Eastern Experiment Station 
in College Park, MD (it later became the College Park 
Research Center and then the Avondale Research Center) 
studied the corrosion and embrittlement of boiler steels. 
This work resulted in numerous publications, including a 
bulletin (2). In the 1940's and 1950's, the corrosion proper- 
ties of Zr (■?), Ti (8), and V (4) were studied extensively. 
These studies contributed greatly to the acceptance of these 
new materials. A bulletin (5) on the corrosion properties of 
Ti is still frequently cited. 

Between 1972 and 1981, the Bureau conducted exten- 
sive research to determine suitable materials for use in con- 
struction of geothermal energy and mineral recovery 
plants. This work resulted in 28 technical publications. Data 
from these studies comprise a large section of a Department 
of Energy publication, "Materials Selection Guidelines for 
Geothermal Energy Utilization" (6), which is the only com- 
piled sourcebook for use by design engineers for material 
selection for these environments. 



Corrosion studies to determine suitable materials for 
use of specific environments and evaluation of new 
materials remain an important area of Bureau research. 
Most of this research is directed at long-range, high-risk 
areas, where an improved fundamental understanding of 
the factors leading to corrosive degradation of materials 
will impact a wide range of problems. This understanding 
ultimately should permit the increased use of domestic 
mineral resources and a concurrent decrease in the demand 
for Cr and other imported metals. These fundamental 
studies have required the development or adaptation of 
numerous analysis and characterization techniques, which 
are described in following sections. 2 Because of the nature 
of the corrosion process, many of those techniques involve 
alteration and/or analysis of the near-surface region. 

In the "Applications" section, two examples are given of 
current research where it is demonstrated that the optimum 
solution to a corrision problem will depend on improvements 
in our basic understanding of the corrosion process. 



2 All citations to the experimental work described in the following sections 
refer to research conducted by the Corrosion and Surface Science research 
group at the Avondale Research Center. These citations are intended to 
describe our approach to developing an understanding of important corro- 
sion processes. 



1 Supervisory research chemist, Avondale Research Center, Bureau of 
Mines, 4900 LaSalle Rd., Avondale, MD 20782. 





Abbreviations Used in This Paper 


°c 


degree Celsius 


K 


kelvin 


M 


molar (concentration) 


m 


molal (concentration) 


mm 


minute 


lim 


micrometer 


N 


normal (concentration) 


nm 


nanometer 


pet 


weight percent 


ppm 


parts per million 


ppt 


parts per thousand 


V 


volt 


yr 


year 



116 



MATERIAL CHARACTERIZATION 



In the early 1970's research was conducted on the use of 
a high-energy ion beam incident on the metal surface (clean 
or corroded) to produce X-rays characteristic of the 
elements present in the first few thousand angstroms of the 
material (7). This technique, known as particle-induced 
X-ray emission analysis (PIXE), is very appropriate for the 
study of corrosion films and has proven very useful in 
numerous studies. (See references 8-10 for examples.) A sec- 
ond technique, Auger electron spectroscopy (AES), which 
can detect elements present in only the first few atomic 
layers of a material, has been utilized in numerous studies of 
corrosion and oxidation on metals (11-12). When combined 
with argon ion bombardment that removes atoms from the 
surface, both the PIXE and the AES techniques can provide 
a depth profile of a material. An example will be shown later 
in which a depth profile of a corrosion film permitted an 
understanding of the role of the various alloying elements in 
forming a very protective corrosion film. 

In addition to PIXE and AES, many other analytical 
techniques are utilized to develop an understanding of the 



corrosion process. Optical metallography, X-ray diffraction, 
scanning electron microscopy (SEM), and scanning 
transmission electron microscopy (STEM) and its associated 
electron diffraction capabilities are available at Avondale 
and are used routinely in these studies. An X-ray photoelec- 
tron spectrometer (ESC A) that was recently installed will 
be used to determine the chemical bonding and/or oxidation 
state(s) of elements in the corrosion films. Other techniques, 
such as secondary ion mass spectrometry (SIMS) and ion- 
scattering spectrometry (ISS), available through private 
service companies, and the electron microprobe at the 
Bureau's Albany Research Center, also have provided very 
useful information. In most cases, no single analytical 
technique can provide the required information; the tech- 
niques are usually complementary. When combined with the 
various electrochemical and corrosion tests, it is possible to 
develop an understanding of the roles of the environment 
and the components of a material in the corrosion process. 



FUNDAMENTAL CORROSION REACTIONS 



Chromium-containing iron-base alloys comprise the 
largest class of corrosion-resistant metallic materials. 
Although much is known about the performance of these 
alloys in a wide range of environments, the roles of impor- 
tant chemical species in the corrosion process on these 
alloys are still not well understood. For example, depending 
on the solution pH and the amount of 2 present, the overall 
cathodic process in the corrosion reaction can be due to 
either reduction of H* or 2 . Intermediates in the fundamen- 
tal reactions, H atoms and oxide or hydroxide ions, can in- 
teract with the corroding metal surface to influence the cor- 
rosion behavior. Previous electrochemical corrosion 
research (13) on an Fe-Cr alloy (Fe-18Cr) in ultra-high- 
purity dilute H 2 S0 4 showed that, in the presence of H 2 , the 
alloy did not corrode, but attained a potential near that of 
the reversible hydrogen electrode. By a cathodic polariza- 
tion of the alloy surface it was possible to induce active cor- 
rosion. A mechanism was proposed (IS) that involved the 
formation of Cr-H species on the surface that controlled the 
evolution of H 2 and the dissolution of the alloy. A more re- 
cent study (14.) showed that the bonding strength of H atoms 
to the alloy surface was a strong function of potential, and 
that the rate of the cathodic process at the corrosion poten- 
tial was controlled by the electrochemical-desorption step, 
H* + e + H - H 2 . 

In many oxidizing environments it has been shown that 
stainless steels exhibit low corrosion rates because of the 
presence of a Cr-rich passivating oxide film. If the steel is 



used in the presence of chloride ions, this passive film can be 
disrupted and serious pitting corrosion will occur. In a re- 
cent study (15), it was shown that the resistance of this 
passivating film to degradation by chloride ions can be im- 
proved by prepassivating the steel in a chloride-free H 2 S0 4 
solution prior to exposure to chloride ions. The rate of 
breakdown of the passive film, as expected, increased with 
increasing chloride ion concentration. The relationship be- 
tween time before breakdown occurred, potential, and 
chloride ion concentration is shown in figure 1 for a Fe-18Cr 
alloy in IN H 2 S0 4 solution. The induction time represents 
the interval between addition of the chrlorde ion and the 
breakdown of the films as evidenced by the open circuit 
potential decaying to the corrosion potential. Similar results 
were observed for 430 stainless steel. 

The understanding that has been gained through these 
fundamental studies and the experimental techniques that 
have been developed are proving useful in many areas of 
current corrosion research. One area of research where in- 
sufficient knowledge exists is that of the mechanism of ac- 
tion of various corrosion inhibitors. Studies are underway to 
determine the effect of both inorganic and organic inhibitors 
on the important corrosion reactions, including H* and 2 
reduction and metal dissolution. The understanding gained 
from these studies should lead to improved, more en- 
vironmentally acceptable inhibitors that will extend the 
lifetime of materials and permit the use of alloys containing 
less Cr in corrosive environments. 



FUNDAMENTAL MATERIALS STUDIES 



A small, but important, portion of our research has been 
to demonstrate that coatings and other surface modification 
techniques can be used to protect materials from corrosion 
or wear and thereby reduce the requirements for certain 
critical materials. A more important use of these techniques 



is to prepare model alloys that either would be very expen- 
sive if made by conventional metallurgical procedures or 
cannot be prepared by other techniques. These alloys permit 
us to study the roles of composition and structure of an alloy 
in improving the corrosion properties. 



117 



INDUCTION TIME, min 
-10 5 



k— 10 3 



Y~ 



r 



10 1 



10 



L20 



30 



0-. 



tffc 



N, 



40 



50 



Ppt 



<& 



& 



^ 



FIGURE 1.— Effect of chloride ion concentration and open circuit potential on time required for breakdown of the passive film 
on Fe-18Cr(J5). 



Research on the preparation of platinum-group-metal 
(PGM) coatings (16-19) demonstrated that these coatings on 
high-temperature alloys such as Mo can be used in place of 
bulk Pt shapes. Research on nitrided low-alloy steels 
showed that these steels exhibited corrosion properties 
equivalent or superior to those of stainless steels in aerated 
chloride-containing solutions (20). 

The use of ion beams (ion implantation) to prepare a 
very thin corrosion-resistant region by implantation of ions 
such as Cr and Ni into a less corrosion resistant material 
was demonstrated in the early to mid 1970's (21-22). In later 
studies, ion implantation was used as a tool to study such 
factors as the role of Cr in reducing the oxidation of Fe 
(23-2U), the effect of Ti, Mo, or Ta on the corrosion fatigue 
behavior of Fe in 0.1AT H 2 S0 4 (25), and the effect of Si, N, or 
Ar on the stress corrosion cracking (SCC) of 316 stainless 
steel in boiling MgCl 2 (26). While Mo and Ta did not affect 
the corrosion fatigue behavior of Fe, Ti reduced the fatigue 
lifetime due to the formation of an imperfect amorphous 
surface layer (25). Nitrogen and argon implantation in- 
creased the likelihood of SCC failure of 316 stainless steel, 
apparently as a result of ion damage and gas coalescence, 
but Si improved the SCC resistance, apparently due to the 
formation of a thin, resilient protective film (26). 



Although it no longer uses this research tool, the 
Bureau is recognized as one of the pioneers in this field (27). 
A wide range of direct applications of ion implantation are 
underway at other laboratories to reduce corrosion and 
wear and to increase the durability of ceramics (27). 

Another technique that can be used to prepare ex- 
perimental alloys with controlled composition and 
microstructure is the use of a laser to melt and mix a surface 
coating with a thin layer (generally < 100 /tin) of a substrate 
material. As shown in figure 2, a thin, apparently uniform 
alloy layer, in this case an Fe-Cr alloy, can be produced by 
this method. The electrochemically determined corrosion 
properties of a series of Fe-Cr alloys prepared by this laser 
mixing technique indicate that there may be unexpected 
spatial nonuniformities in the composition. A STEM study 
of the laser-processed region for these alloys is in progress 
in order to determine if composition and/or structure fluc- 
tuations are present that would explain the corrosion pro- 
perties. 

Another technique for alloy preparation, vapor quench- 
ing, has proven to be particularly useful in our studies to 
determine how alloy composition and structure affect corro- 
sion properties. This technique involves sputtering a target 
material by energetic inert gas ions. The target contains the 



118 




Scale, /urn 



FIGURE 2.— Energy-dispersive X-ray map showing Cr in the cross section of Fe-5Cr substrate with an initial 3-mm-Cr coating 
after laser processing. Alloyed region is 25 to 30 mm thick with an average composition equivalent to Fe-15Cr. 



components of interest either as a metallurgical alloy or as a 
compressed pellet composed of a mixture of the components 
in the proper ratio for the alloy being prepared. The sput- 
tered target atoms are quenched onto the desired substrate. 
The alloy produced may be either crystalline or amorphous, 
depending on such factors as the nature of the substrate, 
the substrate temperature, the rate of deposition, and the 
surface and/or solid state mobilities of the alloy components. 
An example of an alloy prepared by vapor quenching 
that demonstrates the role of structure in determining cor- 
rosion properties is Fe-Zr {28). The Fe-Zr vapor-quenched 



alloys 3 were found to be amorphous over the range of com- 
positions from Fe 9 oZr 1( ) to Fe 33 Zr 67 (28). Electrochemical 
anodic polarization studies (28) showed the Fe^Zr^ alloy to 
be approximately as corrosion resistant as an Fe-18Cr alloy 
and the Fe 33 Zr 67 alloy to be equivalent to pure Zr. All of the 
alloys exhibited a region of reduced anodic current ("passive 
region") over a range of potentials similar to that observed 
for many common stainless steels. A depth profile (fig. 3) 



3 These alloys were prepared by Dr. C. L. Chien, Department of Physics, 
Johns Hopkins University, Baltimore, MD 21218. 



119 




10 15 20 

DEPTH, nm 

FIGURE 3.— Auger electron spectroscopy depth profile of Fe,„Zr 40 amorphous alloy after passivation in IN H 2 S0 4 . 



25 



obtained by AES-ion sputtering of the Fe^Zr^ alloy follow- 
ing formation of the passive film in a 1JV H 2 S0 4 solution 
showed the passive film to be predominantly composed of Zr 
and 0, with the Fe being significantly depleted in the first 
10 nm of the corrosion film. 

It is thus apparent that these alloys behave in a manner 
similar to that of pure Zr because of the formation of a Zr- 
enriched oxide film that resists the acidic environment. This 
behavior is equivalent to that of stainless steels, where the 
passive oxide film is highly enriched in Cr. Also, the lack of 
crystallinity seems to greatly improve the corrosion proper- 
ties compared to what would be expected for a multiphase, 
crystalline alloy over this composition range. 

A vapor-quenched alloy having the composition of com- 
mercial 304 stainless steel also has been prepared. This alloy 
was found to have a body-centered cubic crystalline 
microstructure rather than the face-centered cubic struc- 



ture of the conventionally prepared 304 alloy (29). No amor- 
phous phases were detected for this vapor-quenched alloy. 
Both intergranular and intragranular microvoids, ranging 
from 10 nm to 40 nm in size, were observed in the vapor- 
quenched 304 alloy. These voids, whose population decreas- 
ed with increasing deposition (substrate) temperature, were 
mostly localized near the substrate (29) and are not expected 
to influence the corrosion properties. A transmission elec- 
tron microscope micrograph of a typical alloy exhibiting in- 
tergranular voids is shown in figure 4. 

The capabilities to characterize metallic materials and 
surface corrosion films and to prepare materials of desired 
composition and structure have improved dramatically dur- 
ing this decade. The ability to make optimum material selec- 
tion depends on understanding how material composition 
and structure affect performance. 



120 




FIGURE 4.— Bright-field transmission electron micrograph of a vapor-quenched (at 77 K) 304 stainless steel film 
tergranular voids and small grains. Picture is overfocused to show voids (29). 



e, nm 

exhibiting In- 



121 



APPLICATIONS 



A large number of commercial alloys were evaluated in 
high-temperature geothermal environments typical of 
western hydrothermal resources. These alloys included 
stainless steels (80-36), carbon and alloy steels (30-84, 36), Ni 
alloys (80-84, 87), Cu alloys (81, 83, 88), Ti alloys (80-81, 88-34, 
88), Al alloys (81, 3 A, 38), and Cb and Mo alloys (81, 33, 88). 
Figure 5 shows the effect of Cr concentration on the general 
corrosion of a wide variety of commercially available steels 
in geothermal wellhead brine containing 115,000 ppm CI" 
(about 25 pet total dissolved solids) at pH 5.3 and 215° C. 
The measurements were made by linear polarization on 
"scale-free" surfaces and correspond to an upper limit on the 
rate one would observe in this environment. (Cramer (39-40) 
has described the design and techniques used in the linear 
polarization experiments.) An analysis of the linear polariza- 
tion data showed that corrosion rates vary over more than 
two orders of magnitude. The solid curve represents the 
behavior of Fe-Cr alloys without other alloying elements; 
the cross-hatched area represents stainless steels with 
various additions of Mo and Ni and smaller amounts of other 
elements. Two regions exist where there are appreciable 
benefits from Cr additions. Small additions (2 to 4 pet) 
markedly reduce the corrosion rate compared to that of the 
mild steels. Further additions, up to 12 pet Cr, result in only 
marginal improvements, and there is no effect from the ad- 
dition of other elements such as Mo, Ni, and Cu. On the 
other hand, very substantial reductions in corrosion rate are 
realized in the range of 18 to 29 pet Cr, and these reductions 
are markedly enhanced by the presence of small amounts of 




FIGURE 5.— Dependence of corrosion rate on Cr concentra- 
tion and added Mo, Ni, and Cu for alloys in contact with 
geothermal brine containing 115,000 ppm Cl~ at pH 5.3 and 
215° C. 



Mo and Ni. Longer exposures in this environment showed 
that a number of these alloys, particularly Fe-29Cr-4Mo and 
Fe-29Cr-4Mo-2Ni, have excellent resistance to general cor- 
rosion, crevice and pitting corrosion, and stress corrosion 
cracking and are recommended for use in severely corrosive 
geothermal environments. 

The expertise developed in the material studies in 
geothermal environments has proved very useful in a new 
fundamental study of the behavior of metallic materials in 
high-temperature environments of interest in minerals pro- 
cessing. Hydrometallurgical and pressure hydrometal- 
lurgical processes for extraction, purification, and recovery 
of mineral and metal values frequently use acid sulfate en- 
vironments. Typical processes of interest include H 2 S0 4 
pressure leaching of Ni-Cu and Ni-Co matte, acid pressure 
oxidation of ZnS concentrates, and H 2 pressure reduction of 
Cu from acidic solutions. These acid sulfate solutions are 
corrosive at ambient temperature and even more so at the 
temperatures encountered in pressure hydrometallurgical 
processes. 

Stainless steels have been shown in Bureau research to 
exhibit widely varying corrosion resistance in acid sulfate 
environments at 50° to 250° C and pH 1 to 3. In pH 1, 0.9m 
Na2S0 4 , the ferritic stainless steels 430, Fe-18Cr, and Fe- 
18Cr-2Mo exhibit high corrosion rates at all temperatures. 
However, the austenitic stainless steels 304 and 316L, the 
duplex stainless steel Sandvik 3RE60, and ferritic stainless 
steels containing 25 to 30 pet Cr show a uniform increase in 
corrosion rate with temperature up to approximately 180° 
C, and then a decrease at higher temperatures. In the case 
of the ferritic stainless steels, the decrease is dramatic; cor- 
rosion rates are an order of magnitude lower at 250° C than 
at 180° C. This unexpected corrosion maximum correlates 
with a change in the composition and structure of the corro- 
sion film from a mixed Fe-Cr oxide to one that is basically an 
oxide of Cr. 

Figure 6 shows the alloy surface after the removal of 
the corrosion film for three ferritic stainless steels exposed 
15 days to the pH 1 sulfate solution at 180° and 250° C. All 
of the SEM photomicrographs represent the same 
magnification. The rapidly corroding Fe-18Cr shows no 
evidence that metal dissolution has been altered by the cor- 
rosion film. Other than a slight roughening and the absence 
of crystallographic etch pits, the grains corrode as freely at 
250° C as at 180° C. This is not the case for the other two 
alloys. Both alloys exhibit severe intergranular corrosion 
and localized attack on the grains at 180° C. These forms of 
attack are eliminated at 250° C. Both alloys are only lightly 
attacked. In the case of the Fe-26Cr-3Mo-2Ni, the grain 
boundaries actually appear more resistant to attack than 
the grains themselves. The attack on the Fe-29Cr-4Mo-2Ni 
is even more mild, and no crystallographic features are evi- 
dent. As our understanding of the compositional, structural, 
and thermodynamic factors that govern the formation of 
stable, protective corrosion film in high-temperature solu- 
tions improves, applications of that technology are possible 
to lower Cr containing alloys, to lower and higher 
temperatures, and to erosive conditions. 

In cooperation with the American Iron and Steel In- 
stitute, research is being conducted to determine the effects 
of the mixed acid bath variables on the pickling of commer- 
cial stainless steels. Acid pickling is widely used in the metal 
industry for cleaning annealed and hot-worked stainless 
steel (41). Compositions of pickling solutions are generally 



122 



180° C 



250° C 




Fe-18Cr 




Fe-26Cr-3Mo-2Ni 



mm 




Scale, jum 



Fe-29Cr-4Mo-2Ni 



FIGURE 6.— Scanning electron micrographs following removal of corrosion film for three Cr alloys exposed at 180° C or 250° C 
to deaerated 0.9m Na 2 S0 4 at pH 1. 



123 




CONCENTRATION 



FIGURE 7.— Dependence of dissolution rate on HN0 3 concentration for 304 stainless steel and for Cr-depleted region. Hatched 
region indicates conditions where most efficient pickling would occur. 



chosen for their ability to remove mill scale and alloy- 
depleted surfaces, and to provide an acceptable surface ap- 
pearance. The most frequently used solution, HN0 3 -HF, 
operates by undermining the scale and thus causing it to fall 
off. Simultaneously, the alloy-depleted surface layers 
(reduced Cr concentration compared with that of the bulk) 
are dissolved. These surface cleaning reactions result in an- 
nual losses amounting to several thousand tons of Fe, Cr, 
and Ni and create a sizable disposal problem. The dissolu- 
tion products also interfere with the operation of the pic- 
kling bath. The effects of important parameters such as 
temperature, concentration of HN0 3 and HF, bath chemical 
complex formation, scale and alloy composition, agitation, 
aeration, immersion time, alloy cold work, and dissolved 
metal concentrations are being investigated. The objective 
is to select a set of operating conditions that yields improved 



surface quality of the stainless steels, reduces corrosion loss 
of critical elements, lessens the disposal problem, and ex- 
tends bath life. 

For the two steels currently being studied, alloys 304 
and 430, corrosion and surface analysis studies have shown 
that the alloy dissolution rate increases with increasing HF 
concentration and that, for a given concentration of HF, for 
example, 0.5M HF, the dissolution rate exhibits a maximum 
at approximately 1M HN0 3 . The Cr-depleted region 
dissolves at a much higher rate than the bulk alloy. A 
diagrammatic representation of these experimental obser- 
vations is shown in figure 7. The obvious conclusion that can 
be drawn from this figure is that a region exists where op- 
timum pickling will occur. Such information will enable the 
industry to improve the economics of pickling and to reduce 
the loss of Cr and other important alloying elements. 



CONCLUSIONS 



The selection of the most appropriate alloy for use in a 
given environment can only be made when performance, 
cost, and availability are known. As new environments are 
encountered, efficient techniques are required to determine 
and understand material performance. A fundamental 
understanding of the roles of alloy composition and struc- 
ture in material performance is necessary in order to predict 



service life with respect to material loss by general corro- 
sion or more localized forms of corrosion, such as pitting or 
stress corrosion cracking. Modern surface- and electro- 
analytical techniques and innovative material preparation 
methods permit the determination of mechanisms of cor- 
rosive material loss and of material protection, and allow for 
optimal use of our material resources. 



124 



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in Brine Environments of the Salton Sea Known Geothermal 
Resource Area. Mater. Perform., v. 19, No. 9, 1980, pp. 13-16. 

33. Cramer, S. D., and J. P. Carter. Corrosion in Geothermal 
Brines of the Salton Sea Known Geothermal Area. Ch. in Geother- 
mal Scaling and Corrosion, ed. by L. A. Casper and T. P. Pinch- 
back. ASTM STP 717, 1980, pp. 113-141. 

34. McCawley, F. X., S. D. Cramer, W. D. Riley, J. P. Carter, and 
P. B. Needham. Corrosion of Materials and Scaling in Low Salinity 
East Mesa Geothermal Brines. BuMines RI 8504, 1981, 17 pp. 

35. Carter, J. P., S. D. Cramer, and R. K. Conrad. Corrosion of 
Stainless Steels in the Geothermal Environments of the Salton Sea 
Known Geothermal Resource Area. Reprint230 from Corrosion/81 
(Apr. 6-10, 1981, Toronto, Ontario, Canada). Natl. Assoc. Corro- 
sion Eng., 1981, 15 pp. 

36. Cramer, S. D., J. P. Carter, and R. K. Conrad. Corrosion and 
Scaling of Carbon and Alloy Steels in Salton Sea Geothermal En- 
vironments. Ch. in Solving Corrosion and Scaling Problems in 
Geothermal Systems, ed. by J. P. Carter. Natl. Assoc. Corrosion 
Eng, 1984, pp. 188-208. 

37. Corrosion and Scaling of Nickel Alloys in Salton Sea 

Geothermal Environments. Ch. in Solving Corrosion and Scaling 
Problems in Geothermal Systems, ed. by J. P. Carter. Natl. Assoc. 
Corrosion Eng., 1984, pp. 215-235. 

38. Conrad, R. K., J. P. Carter, and S. D. Cramer. Corrosion of 
Selected Metals and a High-Temperature Thermoplastic in Hyper- 
saline Geothermal Brine. BuMines RI 8792, 1983, 20 pp. 

39. Cramer, S. D., and P. B. Needham, Linear Polarization 
Measurements at High Temperatures in Hypersaline Geothermal 
Brines. BuMines RI 8308, 1978, 15 pp. 

40. Cramer, S. D. Estimation of the Slope of Polarization Curves 
in the Vicinity of the Corrosion Potential. J. Electrochem. Soc, v. 
126, No. 6, 1979, pp. 891-893. 

41. Covino, B. S., J. V. Scalera, and P. M. Fabis. Pickling of 
Stainless Steels-A Review. BuMines IC 8985, 1984, 15 pp. 



BuMines IC 9087: Chromium-Chromite: Bureau of Mines Assessment and Research 



125 



SUBSTITUTES FOR CHROMIUM IN CORROSION- AND 
OXIDATION-RESISTANT STAINLESS STEELS 

By J. S. Dunning 1 



ABSTRACT 



Bureau of Mines research into substitutes for Cr in 
stainless steels is reviewed. In less severe, low-temperature 
environments, steel containing 9 pet Cr with additions of 
Mo, Cu, and V provided aqueous corrosion resistance com- 
parable to that afforded by 18-8 grades of stainless steels. In 
high-temperature, oxidation-resistant applications, Al and 



Si have demonstrated potential for replacing significant 
amounts of Cr. Additions of up to 5 pet Si or Al can replace 
significant amounts of Cr while retaining or even enhancing 
oxidation resistance. Basic studies to determine the role of 
Cr, Si, and Al in providing oxidation protection also are 
surveyed. 



INTRODUCTION 



The production of stainless steels accounts for approx- 
imately 70 pet of the Cr imported for the metals industry in 
the United States. A sizable portion of this is used for AISI 
300 series grades, type 304 in particular. These steels with- 
stand a greater variety of service environments than any 
other commercial metal alloys. This versatility stems from 
resistance to corrosion and oxidation, room-temperature 
and high-temperature strength, excellent ductility and for- 
mability, machinability, weldability, appearance, and ease of 
maintenance. Alloys that do not possess this rare versatility 
are not likely to substitute for stainless steels in a significant 
range of applications. 

The development of new alloys is a slow process, and 
certification of these alloys in critical applications takes 
years of testing after the alloy compositions have been 
finalized. However, the development of alloy substitutes 
that in the event of a Cr supply disruption could be used in 
the less demanding applications of stainless steel could be 
important. Very large tonnages of Cr are used in the less 



demanding applications. Stockpile and recycled Cr could be 
used for critical defense and high-technology process re- 
quirements. Since Cr is currently cheap and readily 
available, there is little incentive for private industry to 
develop substitute alloys, and the responsibility has fallen 
largely to federally funded research. In addition to the 
development of versatile low-Cr substitute alloys, basic 
research on the principles controlling oxidation-corrosion 
behavior in Fe-base alloys is necessary to advance the state- 
of-the-art in developing low-Cr or non-Cr alloys that can 
function effectively in severe environments. 



1 Metallurgist, Albany Research Center, Bureau of Mines, P.O. Box 70, 
Albany, OR 97321. 





Abbreviations Used in 


This 


Paper 


°c 

h 


degree Celsius 
hour 






N 

pet 

ppm 


normal (concentration) 
weight percent 
parts per million 





126 



BUREAU OF MINES RESEARCH ON SUBSTITUTES FOR CHROMIUM 

IN STAINLESS STEELS 



Reduced dependence on imported Cr can best be real- 
ized by finding substitutes for Cr in stainless steel alloys. 
Technical opportunities for reaching this goal are outlined 
below. 

A. Conservation 
Rycycling 

Improved service life of parts 
Improved processing 

B. Partial Replacement 

Performance needs related to application 

C. Complete Substitution 

Bureau research has indicated that, in terms of new alloys, 
complete substitution for Cr is unlikely; partial substitution 
has therefore been the most fruitful research approach. 

As stated above, the stainless steels are versatile 
materials. A substitute alloy will have to possess the same 
versatile traits outlined as follows: 

A. Cost. 

B. Workability. 

C. Wettability. 

D. Machinability. 

E. Corrosion or oxidation resistance. 

F. Room and/or high-temperature mechanical 
properties. 

Any alloy that falls short in one or more of these re- 
quirements may find only limited use as a substitute 
material. Since large tonnages of stainless steel are used in 



such a broad array of applications, it is extremely difficult to 
categorize end uses. Figure 1 is a qualitative representation 
of the tonnages of stainless steel used at various temper- 
atures combined with a qualitative representation of the 
criticality of the application to the economic and military 
well-being of the United States. Very large tonnages of 
stainless steels are used at low temperatures in corrosion- 
resistant applications where plain carbon steels or low-alloy 
steels will not suffice. Typical examples are found in the 
food and transportation industries. At intermediate temper- 
atures, lower tonnages are used, but the applications are 
more demanding in terms of properties. These applications 
are at the heart of high-technology industry such as the 
chemical process and power generating industries. At the 
high end of the temperature spectrum, the quantity of Cr 
used is much less, but uses are critical high-technology and 
military applications, such as turbines and jet engines. 
Stainless steels and high-Cr, Fe-base alloys are currently 
used over this wide temperature spectrum. It is unlikely 
that a universal substitute alloy will be developed that will 
find application over this entire temperature range. Bureau 
research has shown that alloying additions that can 
substitute for Cr to provide corrosion resistance at ambient 
temperature are generally of little help for oxidation 
resistance at elevated temperature, and vice versa (1). Thus, 
technically there is little justification for developing a 
universal substitute. Bureau research is aimed at two 
categories: (1) low-temperature, corrosion-resistant applica- 
tions, and (2) high-temperature, oxidation-resistant applica- 
tions. 



Tonnage 
used 




Low temperature 
Corrosion 
resistance 



Intermediate temperature 
Oxidation resistance and 
strength at temperature 



High temperature 
High performance 
turbine materials 



I 

Criticality 
based on 

substitutes 
available 



FIGURE 1.— Qualitative representation of tonnages of stainless and high-temperature steels. 



I 



127 



SUBSTITUTE OPTIONS FOR CORROSION RESISTANCE 



Low-temperature, corrosion-resistant applications con- 
sume large tonnages of stainless steel and thus present a 
large potential for Cr conservation. For example, if the 
average Cr content could be reduced from 18 pet to 12 pet 
for these applications, several million pounds of Cr could be 
saved annually. 

The literature on alloying elements that modify the cor- 
rosion behavior of Fe-Cr and Fe-Cr-Ni stainless steels has 
been recently summarized (2). Taking the elements that 
have a beneficial effect on corrosion and/or pitting corrosion 
resistance of austenitic stainless steels and eliminating Cd, 
Be, Ag, Re, and Zn on the basis of either toxicity, cost, or 
adverse effect on other properties, we have for consid- 
eration Mo, Ni, Si, Cu, V, and N (1, 3). 

Bureau-sponsored contract research conducted by 
International Nickel Co. showed that a stainless steel con- 
taining 9 pet Cr, with additions of Mo and possibly Cu and 



V, could provide comparable ambient temperature corro- 
sion properties to 18-8 grades of stainless steel in less severe 
environments such as liVH 2 S0 4 , marine environments, and 
10,000 ppm CI" solutions. Mechanical properties, workabil- 
ity, and weldability of these austenitic alloys are all ac- 
ceptable. 

The fact that these alloys are suitable for less severe en- 
vironments should not be taken as an indication of limited 
potential. Large tonnages of stainless steel are used in just 
such applications. Thus, the reduction from 18 pet Cr to 9 
pet Cr is indeed significant. 

Typical additions in the 9-pct-Cr alloys range from 2 to 5 
pet Mo with 2 pet V and 2 pet Cu. Nickel additions in the 
range of 12 to 16 pet are required to maintain an austenitic 
microstructure (4), although Ni requirements can be re- 
duced through minor additions of Mn and/or C. 



SUBSTITUTE OPTIONS FOR OXIDATION RESISTANCE 



The effect of alloying additions on the resistance of 
stainless steels to oxidation has been well documented (2, 5). 
Additions of Al and Si are of primary interest. These two 
elements have the potential for replacing substantial 
amounts of Cr in high-temperature applications. Further- 
more, minor additions of Y, Ca, Ce, and N can be considered 
as candidates to enhance oxidation resistance, but it is not 
likely that any of the four, by itself, can replace a great deal 
ofCr. 

Relatively small additions of Si and Al (up to 5 pet) can 
replace significant quantities of Cr while retaining or even 
improving on the oxidation resistance of 18-pct-Cr steels. 
Aluminum in combination with lower Cr additions also can 
result in enhanced resistance to high-temperature corrosion 
in sulfur-containing environments (6). 

Silicon additions in the range of 3.5 to 4.5 pet with or 
without an Al addition of 1 to 2 pet provides excellent oxida- 
tion resistance in 8- to 10-pct-Cr alloys. 

Aluminum additions to 4 pet with or without Si addi- 
tions of 1 pet provide excellent oxidation resistance in 8- to 
10-pct-Cr alloys. Aluminum additions above 4 pet can 
adversely affect ductility and workability (7). 

A combination of Al and Si performs better than either 
alloying element by itself. 

Additions of Ni, Mn, and C are necessary to retain an 
austenitic microstructure. Chromium is a ferrite stabilizer, 
and Ni, Mn, and C stabilize austenite. The potential Cr 



substitutes -Al and Si-are potent ferrite stabilizers. 
Therefore, to control alloy structure, substitution is usually 
done in terms of the Cr and Ni equivalents: 

Cr equivalent = pet Cr + 2(pct Si) + 5.5(pct Al) 
Ni equivalent = pet Ni + 30(pct C) + 0.5(pct Mn). 

Thus, if Cr is replaced one-for-one by Al or Si, Cr- 
equivalent values will be higher than they are for conven- 
tional 18-pct-Cr stainless steels, and Ni-equivalent values 
would have to be raised accordingly to maintain an 
austenitic structure. 

In addition, as Cr is lowered progressively, the 
austenitic structure becomes more unstable in relation to 
the thermally induced and strain-induced martensite 
transformation. Therefore, there are limits on how far the 
Cr content can be reduced without significantly raising the 
Ni content (and cost) to retain a stable austenitic 
microstructure. Manganese can be added to reduce the re- 
quired Ni, but Bureau research has shown that large Mn ad- 
ditions compromise the oxidation properties of these alloys 
and increase work-hardening rates (8). However, small Mn 
additions (1 to 2 pet) help in stabilizing the austenitic 
microstructure and improve workability. 

Typical compositions currently being studied for high- 
temperature use include Fe-8Cr-14Ni-3.5Si-lAl-lMn for ox- 
idation resistance and Fe-10Cr-14Ni-2Mn-4Al for a com- 
bination of oxidation and sulfidation resistance. 



BASIC STUDIES OF OXIDATION 



While oxidation rates and mechanisms of many pure 
metals and simple alloys have been determined in controlled 
environments, we have not learned to predict the behavior 
of more complex alloys from first principles. As a practical 
example, it is not possible to lower the Cr content of com- 
mercial stainless steels and, either from theory or empirical- 
ly derived relationships, select the concentrations and com- 



binations of Al and Si that will maintain the same oxidation 
protection. 

After a survey of lower Cr (< 10 pet), Fe-base composi- 
tions with Al (0 to 4 pet) and Si (0 to 6 pet) additions, an alloy 
was selected with Al and Si additions in the midrange of the 
above compositions and with oxidation and fabrication prop- 
erties similar to those of AISI 300 series stainless steels. 



128 






An Fe-8Cr-14Ni-3.5Si-lAl-lMn composition was 
studied to determine the role of Cr, Si, and Al in providing 
oxidation protection (9). Scanning electron microscopy, 
X-ray diffraction, microprobe analysis, and Auger spec- 
trometry were used to determine the composition and struc- 
ture of the oxide formed on the alloy as a function of 
temperature and time. The alloy was oxidized in air at 700° 
to 1,000° C for 1 to 1,000 h. The initial protection was de- 
rived from an Al-based Fe and Cr spinel. Later oxide protec- 
tion came from the development of a chromium oxide 
(Cr 2 3 ) layer next to the base metal surface. An outer oxide 
layer also formed which was a mixed composition spinel of 



Cr and Mn (MnOCr 2 3 ). The aluminum that was part of the 
original protective layer eventually (after 100 h) formed a 
pure A1 2 3 precipitate in the base metal. Aluminum in this 
original oxide structure eventually was dispersed into the 
base metal. Later oxidation protection came from develop- 
ment of a Cr 2 3 layer next to the base metal surface. 

Nickel had little effect on the oxidation process, but Si 
played a role in controlling diffusion rates. The rate of ox- 
idation appeared to be controlled by the diffusion of Cr and 
Mn into the metal-oxide interface. The rate of diffusion may 
be controlled by the formation of a thin layer of Si0 2 at this 
interface. 



CONCLUSIONS 



1. Elements that provide low-temperature corrosion 
resistance in low-Cr stainless steel substitutes do not 
necessarily provide high-temperature oxidation resistance. 
The most effective research strategy is to study separate 
alloys for low- and high-temperature application. 

2. To duplicate the versatility of the austenitic stainless 
steels, it is desirable to maintain an austenitic microstruc- 
ture for both low- and high-temperature alloys. 

3. Stainless steels containing 9 pet Cr, with additions of 
Mo and possibly of Co and V, can provide low-temperature 
corrosion properties comparable to 18Cr-8Ni grades of 
stainless steels in less severe environments, such as IN 
H 2 S0 4 , marine environments, and 10,000 ppm CI" solu- 
tions. 



4. In high-temperature applications, additions of Si and/or 
Al of up to 5 pet can replace significant quantities of Cr 
while retaining or enhancing the oxidation resistance typical 
of 18-pct-Cr stainless steels. Good combinations of proper- 
ties have been demonstrated in alloys with 8 to 10 pet Cr, 
and the potential for further reduction in the Cr content has 
been demonstrated. 

5. Basic studies of oxidation kinetics have been successful 
in defining the unique characteristics of Si and Al in com- 
bination with Cr in providing oxidation resistance. 

6. Studies of sulfidation mechanisms have shown that Al 
additions in combination with Cr can drastically improve 
sulfidation resistance at elevated temperatures. 



REFERENCES 



1. Floreen, S. Chromium Substitution in Stainless Steels (con- 
tract JO295070 with INCO Research and Development, Inc.). 
BuMines OFR 110-81, 1980, 73 pp.; NTIS PB 81-235475. 

2. Sedriks, A. J. Corrosion of Stainless Steels. Wiley, 1980, pp. 
70-78, 104-108, 145-150. 

3. Floreen, S. an Examination of Chromium Substitution in 
Stainless Steels. Metall. Trans. A, v. 13a, Nov. 1982, pp. 
2003-2013. 

4. Rhoads, S. C, S. J. Bullard, and M. L. Glenn. Partial Replace- 
ment of Chromium in Austenitic Stainless Steels by Molybdenum, 
Copper, and Vanadium. BuMines RI 8900, 1984, 13 pp. 

5. Peckner, D., and I. M. Berstein (eds.). Handbook of Stainless 
Steels. McGraw-Hill, 1977, pp. 17-10 to 17-18. 



6. Dunning, J. S. A Sulfidation- and Oxidation-Resistant Ferritic 
Stainless Steel Containing Aluminum. BuMines RI 8856, 1984, 15 
pp. 

7. Glenn, M. L., and D. L. Larson. Reduced-Chromium Stainless 
Steel Substitues Containing Silicon and Aluminum. BuMines RI 
8918, 1984, 13 pp. 

8. Benz, J. C, and H. W. Leavenworth. An Assessment of Fe-Mn- 
Al Alloys as Substitutes for Stainless Steels. J. Met., V. 37 Mar. 
1985, pp. 37-39. 

9. Rawers, J. C. Oxidation of a Reduced-Chromium 
Aluminum/Silicon Stainless Steel. Oxidation of Metals, 1986. 



BuMines IC 9087: Chromium-Chromite: Bureau of Mines Assessment and Research 



129 



WEAR-RESISTANT ALLOYS- 
REDUCING CHROMIUM CONTENT AND 
IMPROVING WEAR RESISTANCE 

By Robert Blickensderfer 1 



ABSTRACT 



This report reviews Bureau of Mines research toward 
reducing the wear losses of strategic and critical materials. 
Research on low-alloy steels showed that the Cr in the steel 
does not enhance wear resistance; therefore, Cr may be 
reduced in many applications. In high-Cr white cast irons, 
the spalling wear resistance was improved 24 times over the 
as-cast condition by heat treatment. Welded hard facings in 
the Fe-Mo-Ni-Si system are being investigated in an at- 



tempt to acquire adequate wear resistance in alloys that are 
free of Co and Cr. Plasma-sprayed coatings, using TiB 2 to 
impart wear resistance, are being developed to replace hard 
facings high in Cr, Co, and Ni. Research on grinding ore in 
phosphoric acid waste water showed that Cr is not 
necessarily effective in reducing wear under erosion- 
corrosion conditions. 



INTRODUCTION 



Chromium is an important alloying element for im- 
parting wear resistance to numerous steel alloys, white cast 
irons, and weld hard facings. The so-called abrasion- 
resistant steels typically contain 0.5 to 2 pet Cr. The 
abrasion-resistant, aUoyed white cast irons contain 2 to 28 
pet Cr, and as much or more is used in welded hard-facing 
alloys. 

The Bureau of Mines is particularly concerned about the 
tremendous wear losses that occur in mining and mineral 
processing equipment. Power shovels, excavators, scoops, 
bucket teeth, and other kinds of earth-penetrating equip- 
ment suffer greatly from wear. Some parts wear out com- 
pletely after several weeks or even days of use. The greatest 
tonnages of wear losses, however, occur in crushing and 
grinding equipment. Typically, about 400,000 st of rods, 
balls, and mill liners are consumed annually in the United 
States just for mineral grinding (1). 

The thrust of the Bureau's wear research is toward im- 
proving wear resistance without increasing the Cr content 



of alloys and toward reducing the Cr content of other alloys 
without sacrificing wear resistance. Such results would not 
only conserve Cr but would also reduce operator costs and 
downtime. 



1 Supervisory metallurgist, Albany Research Center, Bureau of Mines, 
P.O. Box 70, Albany, OR 97321. 



Abbreviations Used in This Paper 


cm 


centimeter 


°p 


degree Fahrenheit 


in 


inch 


kg 


kilogram 


m 


meter 


m/g 


meter per gram 


mm 3 


cubic millimeter 


fim 


micrometer 


mm/yr 


millimeter per year 


N 


Newton 


pet 


weight percent 


St 


short ton 



130 



WEAR TEST FACILITIES 



The Bureau's laboratories have a total of 12 wear test 
rigs in use; 10 are for abrasive (including erosive) wear 
tests, and 2 are for repeated impact-spalling wear tests. Ten 
of the units are located at the Albany Research Center, one 
is at the Rolla Research Center, and one is at the Salt Lake 
City Research Center. The wear tests, fully described by 
Blickensderfer (2), include dry-sand, rubber-wheel abrasive 
wear; Taber Abraser; abrasion resistance of refractory 
materials; dry-particle erosive wear; elevated-temperature 
dry-particle erosive wear; low-angle slurry wear; jaw 
crusher gouging wear; ball mill wear; pin-on-drum abrasive 
wear; and high-speed impact gouging. The two repetitive 
impact tests include a ball-on-block impact-spalling test and 
a ball-on-ball impact-spalling test. 



The wear research has several aspects. One is the 
evaluation of existing commercial alloys by laboratory wear 
testing. These data give baseline wear values for future 
comparison and provide unbiased wear values for industry. 
Another part of the research effort is to determine the basis 
of various wear processes in order that wear might be 
reduced through better understanding and more controlled 
application. The third part, which also is the basis for the 
previous two, is to reduce the consumption of Cr. The effect 
of Cr content on the wear of commerical alloys, as well as 
experimental alloys, is studied. This requires the melting, 
casting, fabricating, and heat treating of alloys. A battery of 
analytical methods is used to support this work. 



RESULTS 



LOW-ALLOY STEELS 

The question arose as to whether the Cr used in low- 
alloy steels actually contributes to wear resistance. In 
previous investigations, Haworth (3) and Moore (4) found 
that C was important in providing wear resistance in steels. 
Grinberg (5) found that Cr, W, and V in ferrite did not in- 
crease the wear resistance. 

The 41 different steels that were evaluated by the 
Bureau ranged from pure iron to about 2 pet Cr, Mn, Ni, Si, 
and/or Al, 1.07 pet C, and lesser amounts of Mo, Cu, and S. 
With several different heat treatments, a total of 80 test 
specimens were evaluted by the ASTM dry-sand, rubber- 
wheel abrasive wear test. The results, as reported by 
Tylczak (6), showed that Cr was not effective in providing 
wear resistance to the steels, and furthermore, may even be 
slightly detrimental. Because wear resistance of a given 
alloy composition normally increases with hardness, Cr may 
be useful in thick sections by increasing the depth of harden- 
ing (hardenability). Carbon, on the other hand, was the most 
potent addition for wear resistance. 

The above results are based on a multiple-linear- 
regression program that considered various functional rela- 
tionships and included hardness and the effect of nine 
elements. A simplification of the results for Cr is shown in 
figure 1 for two narrow ranges of C and hardness. Although 
the effect of other alloying elements, such as Mn and Si, can- 
not be shown in this figure, the graph does show that Cr 
does not improve wear resistance. 

The detailed analyses resulted in two equations that 
relate wear, in cubic millimeters, to composition. For 
hardened steels, 



wear = 14 (1 + — ), or wear resistance = - 



C . 



wear 14(1 + C) 



(1) 



and for unhardened steels, 



wear=190-130 -JC -25(Mn) + 110(Mo), (2) 

where the elements are in percent. 

To get the best abrasive wear resistance from a low- 
alloy steel, (1) make the steel as hard as practical, (2) use a 
high carbon level, at least 0.7 to 0.8 pet, (3) use up to 2 pet 
Mn, and (4) add other alloying elements as required, for ex- 
ample, Ni for toughness and Cr or Mo for hardenability. 



ALLOYED WHITE CAST IRONS 

Wear of alloyed white cast irons accounts for significant 
losses of Cr. Although the white cast irons are very abrasion 
resistant, wear by spalling is considerable, and their brit- 
tleness limits them to low-impact applications, as reviewed 
by Dodd (7). To reduce the brittleness compared with that of 
the older NiHard 4 white cast iron, the high-Cr white cast 
irons, containing 15 to 26 pet Cr, were developed. Spalling 
of the high-Cr white cast irons, however, continued to be a 
problem in repeated-impact situations, such as those en- 
countered in ore crushing and grinding equipment. 
Although much was learned by experience and from the 
ball-on-block experiments of Dixon (8), basic causes of spall- 
ing were not understood. The development of the repeated 
impact spalling test by Blickensderfer and Tylczak (9) al- 
lowed systematic studies of impact spalling under controlled 
laboratory conditions. 

The first approach by the Bureau's research was to 
determine whether heat treatments could be found that 
would make white cast irons more resistant to spalling. 
Figure 2 shows the effect of heat treatment on the spalling 
life of a commercial white cast iron containing 17 pet Cr. It 



o 

-z. 
< 

h- 

en 

LU 

cr 

rr 
< 

UJ 



0.04 

.03 
.02 

.0 1 



0.90 to 1.05 pet C 
HB 720 to 861 




0.23 to 0.33 pet C 
HB 453 to 512 • 



Cr, pet 

FIGURE 1.— Effect of Cr on wear resistance of hardened 
low-alloy steels. Three-body, dry-sand, rubber-wheel abrasive 
wear, 133-N load, 1,436-m wear path. 



131 



is typical of the results for other high-Cr white cast irons 
studied. The balls in the as-cast condition had the shortest 
spalling life, or least spalling resistance, less than 10,000 im- 
pacts. The subcritical heat treatments at 1,100° and 1,200° 
F produced excellent spalling resistance, with lives of about 
200,000 impacts. The reaustenized balls were intermediate 
in spalling. Thus, for only 11 different heat treatments, the 
spalling rate differed by a factor of 24. But how did the heat 
treatments affect abrasive wear? 

The abrasion resistance was affected much less by heat 
treatment, but still by a factor of 3.1. The relation found be- 
tween spalling resistance and abrasion resistance (fig. 3) is 
more pertinent than either of the individual relationships. It 
is apparent from the graph that spalling resistance is gained 
at the expense of abrasion resistance and vice versa. From 
this relationship, a heat treatment may be selected that will 
provide the correct balance between spalling resistance and 
abrasion resistance for the particular application. The net 
results of this investigation will be to increase the life of the 
high-Cr cast irons and thereby reduce Cr consumption. 

The second approach to the research on white cast irons 
was to attempt to improve the toughness and abrasion 
resistance of the relatively low Cr NiHard 4 by alloy 
modification. NiHard 4, containing 8 to 10 pet Cr, is widely 
used in mineral processing equipment under limited impact 
conditions. The impact resistance, as well as the abrasion 
resistance, is generally less than that of the high-Cr white 
cast irons. In the research, the composition of NiHard 4 was 
modified by reducing the Si from the normal 1.6 to about 1.1 
pet, increasing Mn from the normal 0.7 to 2 pet, and adding 
0.8 pet Mo. As seen in table 1, not only was the toughness in- 
creased, the abrasion resistance was improvpH 




50 IOO 150 200 

NUMBER OF IMPACTS, thousands 



250 



FIGURE 2.— Effect of heat treatment on spalling life of high- 
Cr white cast iron. Life is for 100-g loss; each * donotes 
breakage of a ball. In the following numerical code, S = sub- 
critical and R = reaustentized. 
1. As-cast 



2. 


Sat 1,000° 


F 






3. 


Sat 1,100° 


F 






4. 


Sat 1,200° 


F 






5. 


Rat 1,750 c 


F 






6. 


Rat 1,850° 


F 






7. 


Rat 1,950° 


F 






8. 


Rat 1,850' 


plus 


Sat 850° 


F 


9. 


Rat 1,850° 


plus 


Sat 900° 


F 


10. 


Rat 1,850' 


plus 


Sat 950° 


F 


11. 


Rat 1,850° 


plus 


Sat1,00C 


I" 



TABLE 1.— Effect of modified composlt 


on of NiHard 4 


Alloy 


Impacts on block 
to fracture' 


Abrasion 
resistance, 2 m/g 


NiHard 4 

Modified' 


3,400 
> 100,000 


7,800 
22,000 



'1.8-kg ball dropped 3.5 m onto block, 5 cm thick. 
2 Dry-sand, rubber-wheel test, 133-N load, 1,435 m. 
Both alloys received the same heat treatment. 



WELDED HARD FACINGS 

The research approach was to seek an Fe-based, weld- 
ed, hard facing that contained no Cr or Co and had 
reasonably good wear resistance. Present wear-resistant, 
commercial hard-facing alloys are based on either a work- 
hardenable Mn alloy or a high-Cr white cast iron, a Cr-Co 
alloy, or a Cr-Ni-Co alloy in which carbide particles provide 
the wear resistance. The Bureau investigated the potential 
of intermetallic precipitates for providing wear resistance. 
The Fe-Mo-Ni system was chosen because these elements 
are not strategic and the intermetallic phases exist over a 
wide range; namely, about 15 to 50 pet Ni and Mo. 

Because this is a relatively new area of research, a con- 
siderable effort was required to obtain information on phase 
identification, solidus temperatures, and welding param- 
eters. The effects of adding up to 1 pet C and up to 5.4 pet Si 
also were evaluated. Specimens were prepared by 
submerged-arc welding on 2-in-thick mild steel plate, using 
Mo-Ni powder additions and an Fe-Mo-Ni filler wire. Addi- 
tional information was reported by Scholl (10). 

Abrasive wear by pin wear tests of the welds showed 
that none was as wear resistant as commercial high-Cr hard 




°- 100 200 300 400 500 600 

ABRASION RESISTANCE, 
meters per gram loss 

FIGURE 3.— Relationship between abrasion resistance and 
spalling resistance of a high-Cr white cast iron. Numbers refer 
to heat treatments in figure 2. Abrasion is by 105-mm garnet, 
2-body, 66.7-N load. 



132 



facing. The amount of wear of the experimental weld alloys 
did not correlate with hardness, but the wear resistance did 
increase as the Mo and Ni contents were increased. The 
microstructural constituents and morphology affect wear in 
some ways not fully understood. The lamellar eutectic 
microstructure decreases wear resistance; whereas complex 
multiphase intermetallics in an austenitic matrix improve 
wear resistace. The weld hard facing with the best wear 
resistance to date was an Fe-20Mo-15Ni-5.4Si composition. 
It possessed a multiphase microstructure with at least two 
eutectics and two intermetallics in a matrix of Fe-Ni 
austenite. The pin wear resistance of 158 m/g was 
equivalent to that of a heat-treated, high-Cr white cast iron, 
even though the hardness was only HRC (Rockwell C) 40. 



PLASMA-SPRAYED COATINGS 

Plasma spraying, as a method of applying hard surfac- 
ings, has potential for forming alloys that cannot readily be 
achieved by welding. The research approach, carried out at 
the Bureau's Rolla Research Center by Mcllwain and 
Neumeier (11), is to provide wear resistance by the addition 
of TiB 2 to an Fe-base, Cr-Ni alloy. The alloy is intended to 
replace Co-based hard-facing alloys and also may replace 
high-Cr white iron hard facings. 

Powders are prepared by mechanical alloying of TiB 2 with 
elemental powders Fe, Cr, and Ni, plus lesser amounts of C, 
Mn, Mo, W, Si, and Cb. Blended powders are sprayed onto 
steel by a plasma arc gun using argon-hydrogen as the 
plasma gas and argon as the carrier gas. The resulting 
coatings contain a network of oxides, carbides, and fine 
precipitates and have low porosity. The optimum TiB 2 con- 
tent is about 5 pet. The abrasive wear resistance and 
adhesive wear resistance appear to be superior to those of 
plasma-sprayed Stellite 6. Other properties, such as hot 
hardness, where Stellite 6 excels, are being compared. The 
bond strength to the steel base needs to be improved, and 
research is continuing on this problem. 



ABRASION-CORROSION OF HIGH ALLOYS 

The approach is to determine whether high alloys, such 
as Ni-based alloys and stainless steels, are justified for use 
where abrasion occurs simultaneously with corrosion. It is 
known that high-Ni alloys and stainless steels resist most 
acids. However, when abrasion occurs simultaneously with 



corrosion, the passivated protective film can be destroyed as 
fast as it forms, and the question arises whether the alloy 
additions are worthwhile for reducing the overall wear. 

Tests were carried out by the Bureau in a laboratory 
ball mill by grinding phosphate rock in phosphoric acid 
waste liquid with alloy test balls. The results, reported by 
Singleton and Blickensderfer (12), are summarized in figure 
4. The nickel alloys and stainless steels are resistant to cor- 
rosion but wear significantly when abrasion is combined 
with corrosion. The alloyed white cast irons, normally very 
abrasion resistant, suffered the highest wear rate under the 
combined action of abrasion and corrosion. The low-alloy, 
high-C steel, under the given conditions, is the most cost- 
effective material. This example shows that some alloys 
containing relatively little Cr may actually wear less under 
certain corrosive wear conditions than alloys containing 
significant amounts of Ni and Cr. 



Hastelloy 

C-276 

Incoloy 

825 

Cronifer 

I7I3LCN 

lllium P 

316 stainless 
steel 

NiResist 

NP599 stain- 
less steel 
CA6NM stain- 
less steel 

Cr-Mo white 
iron 

NiHard 4 

NiHard I 

Commercial 
ball 




a 



Erosion-corrosion, 
60-cm ball mill 
with acid liquor 

3 Erosion, 60-cm boll 
3 with water 

, Static corrosion 
in acid liquor 



20 30 40 50 

WEAR RATE, mm/yr 



60 



70 



FIGURE 4.— Wear and corrosion of 12 alloys during 
laboratory milling of phosphate rock. 



133 



REFERENCES 



1. Nass, D. E. Steel Grinding Media Used in the United States 
and Canada. Paper in Symposium, Materials for the Mining In- 
dustry (Vail, CO, July 30-31, 1974). Climax Molybdenum Co., 
Golden, CO, 1974, pp. 173-188. 

2. Blickensderfer, R., J. H. Tylczak, and B. W. Madsen. 
Laboratory Wear Testing Capabilities of the Bureau of Mines. 
BuMines IC 9001, 1985, 36 pp. 

3. Haworth, R. D., Jr. The Abrasion Resistance of Metals. Trans. 
Am. Soc. Metals, v. 41, 1949, p. 819. 

4. Moore, M. A. The Relationship Between the Abrasive Wear 
Resistance, Hardness and Microstructure of Ferritic Materials, 
Wear, v. 28, 1974, pp. 59-68. 

5. Grinberg, N. A., L. S. Livshits, and V. S. Shchebakova. Effect 
of Alloying of Ferrite and Carbide Phase on the Wear Resistance of 
Steels. Metal Sci. and Heat Treatment, v. 13, No. 9-10, Sept.-Oct. 
1971, pp. 768-770. 

6. Tylczak, J. H. Correlating Alloy Composition to Wear in Low- 
Alloy Steels. Wear of Materials 1985, ed. by K.C. Ludema. ASME, 
1985, pp. 73-78. 



7. Dodd, J. Progress in the Development and Use of Abrasion 
Resistant Alloy Irons and Steels in the Mining Industry. Soc. Min. 
Eng. Trans., v. 270, 1981, 8 pp. 

8. Dixon, R. H. T. Some Effects of Heat-Treatment Upon the 
Impact-Fatigue Life of Ni-Hard Grinding Balls. J. Iron and Steel 
Inst., v. 197, Jan. 1961, pp. 40-48. 

9. Blickensderfer, R., and J. H. Tylczak. A Large-Scale Impact 
Spalling Test. Wear, v. 84, No. 3, 1983, pp. 361-373. 

10. Scholl, M., W. E. Wood, and R. Blickensderfer. Intermetallic- 
Hardened Weld Overlays for Abrasion Resistance. Presented at 
the 65th Annual AWS Convention, Am. Weld. Soc., Dallas, TX, 
Apr. 8-13, 1984, 12 pp.; available from M. Scholl, OR Grad. Ctr., 
Beaverton, OR 97006. 

11. Mcllwain, J. F., and L. A. Neumeier. Plasma-Sprayed Iron- 
Based Wear-Resistant Coatings Containing Titanium Diboride. 
BuMines RI 8984, 1985, 18 pp. 

12. Singleton, D. J., and R. Blickensderfer. Wear and Corrosion 
of 12 Alloys During Laboratory Milling of Phosphate Rock in 
Phosphoric Acid Waste Water. BuMines RI 8919, 1985, 16 pp. 



BuMines IC 9087: Chromium-Chromite: Bureau of Mines Assessment and Research 



135 



BUREAU OF MINES RESEARCH RELATED TO 
REFRACTORIES CONTAINING CHROMIUM 

By Arthur V. Petty, Jr. 1 




ABSTRACT 




Past research at the Bureau of Mines directed toward 
reducing the quantity of imported refractory-grade 
chromite, included a study of the recycling of waste refrac- 
tory furnace linings. Samples of used magnesia-chromite 
refractories removed from steel furnaces and copper 
smelters were beneficiated to remove metal and other con- 
taminants. Refractories produced from recycled argon- 
oxygen decarburization (AOD) linings compared favorably 
with conventional commercial magnesia-chromite refrac- 
tories of similar composition. Slag resistance was superior 
for the recycled brick. 



The high-temperature modulus of rupture (MOR) and 
hot-load properties of domestic periclase grain, used in 
magnesite refractories, were improved by adjusting the 
calcium-to-silica ratio and/or by minor additions of Zr0 2 or 
Mn0 2 . Additions of minor amounts of soluble salts or oxides 
to both MgO and A1 2 3 brick dramatically improved their 
high-temperature properties -particularly hot MOR and 
slag resistance. These improved refractories, produced 
from domestic resources, could substitute for magnesia- 
chromite refractories in many applications. 



INTRODUCTION 



Virtually all chromite used in the United States is im- 
ported, and approximately 20 pet of these imports are used 
in the production of refractories, primarily for the steel, 
copper, glass, and cement industries (1). Chromite ore, in 
combination with magnesia, is the primary constituent of 
these refractories. Approximately 300,000 st of chromite- 
containing refractories (chromite contents ranging from 10 
to 90 pet) are consumed annually in the United States. This 
represents an average rate of consumption of 7.5 lb/st Cu 
produced (2) and 4.9 lb/st steel produced (S). 

Bureau of Mines research during the past 6 yr related to 
reducing the quantities of imported refractory-grade 
chromite can be categorized into three general areas: 

1. A study of the recycling of magnesia-chromite refrac- 
tories used to line steel and copper furnaces. 

2. Improvement of the high-temperature properties of 
domestic magnesite grain and refractories. 



3. Introduction of Cr into alumina refractories using solu- 
ble Cr,0 3 . 



1 Supervisory ceramic engineer, Tuscaloosa Research Center, Bureau of 
Mines, P.O. Box L, University, AL 35486. 



Abbreviations Used in This Paper 


°C 


degree Celsius 


cm 2 


square centimeter 


g/cm 3 


gram per cubic centimeter 


in 


inch 


in 2 


square inch 


in/(in-°C) 


inch per inch • degree Celsius 


lb/ft 3 


pound per cubic foot 


lb/st 


pound per short ton 


pet 


weight percent 


psi 


pound per square inch 


st 


short ton 


y 


year 



136 



RECYCLING OF MAGNESIA-CHROME REFRACTORIES 



STEEL FURNACE LININGS 

Samples of waste magnesia-chromite refractories from 
argon-oxygen decarburization (AOD) and electric steel- 
making operations were obtained from two steel producers 
in Ohio and Pennsylvania (4-5). The samples of waste refrac- 
tories consisted of whole and parts of used refractory brick. 
Some of these brick were partly enclosed in metal casings, 
others had metal and slag readily visible in cracks, and some 
were contaminant-free. 

The waste refractories were crushed, screened, and 
magnetically separated. The handpicked metal casings and 
the magnetic product from the magnetic pulley were com- 
bined and accounted for 1.3 and 4.5 pet of the total weight 
received for the AOD and electric furnace waste refrac- 
tories, respectively. 

Chemical analyses of the head samples from each waste 
refractory and of a commercial refractory brick are listed in 
table 1. These analyses indicate that the waste refractories 
had compositions similar to that of an unused commercial 
brick. 

Energy-dispersive X-ray analysis showed only Mg, Cr, 
Al, Fe, Si, and Ca as the major elemental constituents of the 
samples. However, traces of Mo, S, V, and Ti were also 
observed in the AOD furnace sample, and Ti and Zn were 
observed in the electric furnace samples. Semiquantitative 
spectrographic analyses indicated that trace amounts of Ag, 
Co, and Ni were also present. 

X-ray diffraction (XRD) analyses were made of each 
sample for mineralogieal determinations. XRD patterns 
were also valuable in determining that no significant phase 
changes occurred in the refractory grain during furnace 
operations that might alter the refractory properties of the 
beneficiated refractory grain (chromite concentrate). 
Chromite [(Fe 2 *, Mg 2 *)0-(AP, Cr 3 *, Fe 3+ ) 2 3 ], periclase 



(MgO), and minor amounts of forsterite (Mg 2 Si0 4 ) were 
identified in all the samples. 

Table 2 lists the chemical analyses of chromite concen- 
trates beneficiated at minus 6-, minus 28-, and minus 
65-mesh for each of the three starting waste materials, and 
for samples prepared from two commercial bricks. Both 
Si0 2 and CaO were slightly higher in the beneficiated 
materials than in the commercial brick. No "free" lime, pre- 
sent as CaO, was detected by chemical analysis in any of the 
samples. In commercial magnesia-chromite refractories, the 
Cr 2 3 , Fe 2 3 , MgO, and A1 2 3 contents vary over wide 
limits depending on the source of the chromite ore and the 
chromite-periclase ratio. The variation of these oxides in the 
materials tested falls well within these ranges. 

Preliminary refractory properties of small samples fired 
at 1,500° C are shown in table 3. These results indicate that 
samples produced from the beneficiated materials compare 
favorably to similar test specimens prepared from commer- 
cial refractory grain using the same procedure. 

Beneficiated samples of the AOD and electric steel fur- 
nace refractories were shipped to a commercial refractory 
manufacturer for producing full-size brick. Portions of three 
size fractions were recombined, and suitable binders were 
added. to allow pressing of approximately sixty 9- by 4V2-by 
3-in brick. 

No difficulty was encountered in pressing and burning 
the brick produced from beneficiated AOD linings. 
However, because of the high calcium content of the 
beneficiated electric arc furnace lining, the brick produced 
from this material hydrated and cracked during drying. 
Because of the hydration cracks present in the bricks pro- 
duced from electric steel furnace refractories, they were not 
subjected to further refractory evaluation. Samples of the 
recycled AOD refractory brick were prepared for additional 
testing of their refractory properties, including cold 



TABLE 1.— Chemical analysis of waste refractories 



Sample 



Chemical analysis, pet 



Cr 3 3 



MgO 



AIX> 3 



CaO 



Fe,0, 



SiO, 



Fe' 



Electric furnace: 

Lining A 

Lining B 

AOD furnace 

Commercial brick No. 1 



15.0 
15.2 
16.3 
14.5 



56.7 
60.9 
59.8 
63.8 



10.8 
9.7 
6.5 

13.2 



5.6 

1.5 

3.0 

.7 



8.8 
9.9 
10.8 
6.3 



3.0 
2.3 
3.1 
1.5 



4.5 

NAp 

1.3 

NAp 



NAp Not applicable. 

'Removed from minus 1-in crushed materials before analysis. 



TABLE 2.— Chemical analysis of beneficiated waste refractories reported as oxide equivalents 



Sample 


Particle size of beneficiated 
material, mesh 


Chemical analysis, pet 


Cr 2 3 


MgO 


Al 2 3 


CaO 


Fe 2 3 


Si0 2 


AOD furnace lining 




16.1 
16.1 
16.1 

14.9 
15.2 
15.1 
15.5 
15.4 
15.4 

14.5 
20.7 


59.0 
60.3 
58.7 

57.9 
56.8 
55.5 
60.7 
61.5 
60.8 

63.8 
49.4 


6.5 

7.2 
6.5 

10.4 
12.4 
9.8 
9.4 
10.7 
10.4 

13.2 
17.9 


2.6 
3.4 
2.6 

5.2 
4.5 
5.2 
1.8 
2.0 
2.0 

.7 
.6 


11.0 
10.5 
10.4 

9.1 
8.2 
8.6 
8.6 
9.3 
9.4 

6.3 
9.4 


3.5 


Minus 28 


2.9 




Minus 65 


3.5 


Electric furnace: 
Lining A 




3.4 




Minus 28 . . 


3.0 




Minus 65 


3.5 






1.8 


Minus 28 . . 


2.0 




Minus 65 . . 


1.7 


Commercial brick: 

No. 1 


NAp 


1.5 


No. 2 


NAp . 


2.0 









NAp Not applicable. 

'Magnetically separated using Davis tube magnetic separator. 

'Magnetically separated using Carpco low-intensity magnetic separator. 



137 



TABLE 3.— Refractory properties of chromite concentrates and commercial refractory bricks 


Sample 


Particle size of beneficiated 
material mesh 


MOR' at 1,350° C, psi 
(av of 6 bars) 


Bulk density, g/cm 3 
(av of 3 bars) 


Apparent porosity, pet 
(av of 3 bars) 


AOD furnace lining 


Minus 6 


1,000 
750 
850 

2,200 
1,750 
3,000 
1,450 
1,150 
1,400 

700 
1,050 


2.9 
2.8 
2.9 

3.1 
3.0 
3.2 
2.7 
2.9 
2.9 

2.7 
2.7 


23 9 




Minus 28 


25 1 




Minus 65 


23 1 


Electric furnace: 
Lining A 


Minus 6 


28 6 




Minus 28 


28 




Minus 65 


27 1 


Lining B 


Minus 6 


25 3 




Minus 28 


29 3 




Minus 65 


29 


Commercial brick: 
No. 1 


Minus 65 


27 2 


No. 2 


Minus 65 


27 2 









'Modulus of rupture. 



crushing strength, modulus of rupture (MOR) at 1,500° C, 
hot load, thermal shock resistance, and thermal expansion. 
These data are summarized in table 4 along with manufac- 
turers' data for two commercial refractories. 

The relatively low MOR value obtained for the recycled 
brick at 1,500° C and the corresponding high percentage 
change measured by the hot-load test at 1,750° C are due to 
the relatively low initial firing temperature for these brick. 
When refractories of this type are fired, a glassy-bond phase 
is present between the more refractory periclase and Cr- 
spinel grains up to at least 1,500° C. When refractories are 
fired to higher temperatures (> 1,700° C), a direct bond is 
formed between the periclase and Cr-spinel grains, accom- 
panied by a substantial decrease in the amount of glassy 
phase present at the grain boundaries. This decrease results 
from a redistribution of the silica, which reacts with MgO to 
form forsterite and with CaO to form 2CaO*Si0 2 , both of 
which have high melting points. Hot-load tests were 
repeated for brick after firing to 1,730° C, and deformation 
averaged only minus 1.55 pet, compared with the minus 
6.20 pet reported for samples fired to 1,450° C. 

The slag resistance of recycled AOD refractories was 
evaluated using a rotary slag-test apparatus developed at 
the Bureau's Tuscaloosa Research Center (6-7). Tests were 
conducted using a highly reactive basic oxygen furnace 
(BOF) slag having the composition shown in table 5. Com- 
mercial refractory brick No. 2 was included in the test for 
comparative purposes. 

Average area change for the recycled AOD refractory 
was 3.00 cm 2 , compared with 3.64 cm 2 for the commercial 
refractory. The smaller change for the recycled brick would 
indicate superior resistance to slag corrosion and/or erosion. 



COPPER SMELTER LININGS 

Three copper smelters in Arizona supplied samples of 
used magnesite-chromite refractories from converter and 
reverberatory furnaces (S). The as-received samples con- 
sisted of whole and partial bricks. Metallic copper was visi- 
ble in the refractories. 

The waste refractories were crushed to pass a 1/4-in 
screen, and a product recovered by handsorting was essen- 
tially metallic copper that could be recycled directly to the 
copper smelting furnace. This product accounted for 0.5, 
0.4, and 1.2 pet of the total weight received for samples A, 
B, and C of table 6, respectively. 

Chemical analysis of commercial brick of the same type 
as those used by the copper smelters and those of each head 
sample are presented in table 6. 



TABLE 4.— Refractory properties of recycled waste AOD 
refractory lining and commercial brick of similar composition 



Properties' 


Beneficiated 
AOD lining 


Commercial 
brick 


Apparent porosity pet. . 

Bulk density g/cm 3 . . 

Cold crushing strength ....psi.. 

Modulus of rupture psi. . 

Load test at 25 psi 

(deformation) pet . . 

Spalling resistance index 

Thermal expansion . . .in(in-°C). . 
Slag resistance (area loss) cm 2 .. 


15.4 
3.2 

12,000 
! 150 

"1.55 

7.4 

"0.1 1x10-" 

3.0 


16.0-19.0 

3.1 

4,000-6,000 

3 600-1,200 

( s ) 
NA 
NA 
3.64 



NA Not available. 

'All tests were according to ASTM specifications. 

'At 1,500° C. 

3 At 1,480° C. 

"For brick fired to 1,730° C. 

Negligible deformation under load to 1,800° C. 

"For brick fired to 1,450° C. 



TABLE 5.— Chemical analysis of slag used in rotary slag test, 
percent 

SiO : 33 

CaO 33 

Fe s 3 20 

Al 2 3 4 

MgO 5 

MnO __5 

Total 100 



TABLE 6.— Chemical analyses of magnesia-chromite waste 
refractories and magnesia-chromite brick, percent 





Sample 


Commercial 




A 


B 


C 


brick No. 1 


Cr;0 3 


17.9 

35.4 

14.7 

.8 

11.0 

4.1 

6.4 


18.1 

46.2 

15.9 

.8 

9.4 

3.6 

3 


18.7 

38.7 

16.3 

.6 

11.0 

3.6 

5.2 


21.7 


MgO 

AI 2 Oj 


46.3 
15.9 


CaO 

Fe 2 3 


.7 
11.9 


SiO : 


3.5 


Total Cu' . 










'Includes copper recovered in screen oversize products. 



X-ray diffraction analyses identified periclase (MgO), 
chromite [(Fe 2 % Mg 2+ )0-(Al 3 ', Cr 3+ , Fe 3+ ) 2 3 ], and minor 
amounts of forsterite (Mg 2 Si0 4 ) in all the samples. Traces of 
cuprite (Cu 2 0) were also detected in samples A and B. 

From microscopic examinations of the size fractions, it 
was ascertained that most of the contaminants (copper ox- 
ide, copper sulfides, and metallic copper) were liberated 
from the refractory grain between 65 and 100 mesh. 



138 



Magnetic separation was used to remove copper matte. 
At high magnetic field intensities, the chromite also 
reported with the matte in the magnetic fraction. As a 
result, all magnetic separations were made with a low- 
intensity magnetic field to remove the matte without at- 
tracting the chromite. A Davis tube low-intensity wet 
magnetic separator 2 was selected for this purpose. 

In flotation tests, sodium isopropyl xanthate (collector), 
sodium silicate (dispersant), and pine oil (frother) were add- 
ed at rates of 0.1, 3.0, and 0.16 lb/st respectively. Flotation 
resulted in chromite concentrates having the chemical 
analyses shown in table 7. 

The copper concentrates would be of sufficient grade to 
be recycled to copper smelting furnaces. This represents an 
87-pct recovery. 

Table 8 shows the 1,350° C MOR, bulk density, and ap- 
parent porosity values for a chromite concentrate from 
magnetic separation and froth flotation along with samples 
prepared from two commercial bricks. As shown, MOR 
values for samples fired to 1,500° C are low; however, when 
the samples were fired to 1,700° C (typical for direct-bonded 
mag-chrome refractories), their MOR values were higher 
than those of the standard samples produced from commer- 
cial bricks. 

As previously stated, in order to liberate the majority of 
copper and allow removal by magnetic separation and froth 
flotation, it was necessary to grind the waste copper refrac- 
tory linings to minus 65 mesh, which creates an additional 
problem in the recycling of the material. Preliminary sinter- 
ing of the concentrate would be required to obtain particle- 
size distribution needed for refractory brick fabrication. 
Beneficiation by leaching offers the only feasible alternative 



for lowering the copper content to acceptable levels in a 
coarser material. This may increase the cost of benefication, 
and any advantages would have to be weighed against the 
cost of prefiring the minus 65-mesh material to form a 
refractory grain. 



TABLE 7. 


—Chemical analyses of chromite concentrates from 
continuous flotation testing, percent 




Test 1 


Test 2 


Test 3 


Cr 2 2 


21.4 
43.4 
17.0 

.2 
10.6 
ND 

.2 


23.7 
42.4 
18.0 

.2 
10.6 
ND 

.2 


21.9 


MgO 

Al 2 3 


43.7 
17.2 


CaO 

Fe 2 3 


.3 
10.5 


SiO, 


ND 


Cu 


.2 



ND Not determined. 



TABLE 8.— MOR (1,350° C), bulk density, and apparent 
porosity values for a beneficiated copper refractory fired to 
1,500° and 1,700° C and commercial brick (as-received) 





MOR at 


Bulk 


Apparent 


Sample 


1,350° C, 


density, 


porosity, 




psi 


g/cm 3 


pet 


Beneficiated material:' 








Fired to 1,500° C 


165 


2.50 


31.7 


Fired to 1,700° C 


1,500 


2.77 


28.5 


Commercial brick (as- 








received) 








No. 1 


700 


2.70 


27.2 


No. 2 


1,050 


2.70 


27.2 



'Beneficiation by flotation, magnetic separation; beneficiation product 
minus 65-mesh. 



IMPROVED MAGNESIA REFRACTORIES 



Magnesia materials are used extensively in basic oxygen 
and electric arc steelmaking refractories. Greater use of 
high-magnesia materials in problem areas such as the slag- 
metal interface is limited owing to the superior properties of 
other materials, such as magnesia-chromite, which require 
imported chromite. 

In the United States raw materials for magnesia refrac- 
tories are generally mined as magnesite or processed 
chemically from brines or seawater as periclase grain. If 
techniques could be developed to improve magnesia brick 
properties, their increased usage could result in a decreased 
importation of critical raw materials. 

IMPROVED PERICLASE GRAIN 

The chemical analyses of periclase raw materials used 
for this study (9) are shown in table 9. Two of the periclase 
materials were produced from seawater, two from brines, 
and one from a natural magnesite. Reagent-grade oxide 
powders (minus 200 mesh in size) of Mn0 2 , Zr0 2 , CaO, and 
Si0 2 were used as additives to produce calcined grain hav- 
ing optimized hot-MOR, hot-load resistance, and slag 
resistance properties. 

Small additions of calcia or silica were made in order to 
adjust the C-S ratio (CaO-Si0 2 ), and small quantities of 
either Mn0 2 or Zr0 2 were added as shown in table 9. 



High-temperature properties of full-sized MgO bricks 
made from modified grain and fired to 1,730° C are com- 
pared in table 10 with those for commercial refractories 
fired to the same temperature. All of the 1,300° and 1,500° 
C MOR values for the five optimized periclase materials 
were signifcantly higher than the value obtained for a 
98-pct-MgO commercial refractory. All five of the optimized 
periclase materials exhibited less hot-load deformation at 
1,700° C than that obtained for the 98-pct-MgO commercial 
refractory. The 1,650° C BOF slag resistances of the op- 
timized MgO bricks were similar to that obtained for the 
commercial 98-pct-MgO refractory, with one value (that for 
B-l) better than for the commercial bricks. 



TABLE 9.— Partial chemical analyses of periclase raw materials, 
and additives to produce optimized periclase grains 



2 Reference to specific products does not imply endorsement by the Bureau 
of Mines. 



Analysis, pet: 

MgO 

Al 2 3 

CaO 

Fe,Oj 

Sid, 

B,0, 

Additives, pet: 

Mn0 2 

Zr0 2 

C-S ratio: 

Raw materials . . 

Optimized grains 



Sample No. and source 



B-1, B-2, M-1, natural S-1, S-2, 

brine brine magnesite seawater seawater 



95.3 
0.20 
0.61 
0.61 
0.64 
0.11 


2.0 

0.95 
2.5 



95.9 
0.13 
2.30 
0.40 
0.56 
0.02 



1.0 

4.11 
3.0 



93.5 
0.44 
3.30 
0.64 
1.30 
0.02 


1.0 

2.54 
3.0 



97.4 
0.12 
0.89 
0.46 
0.60 
0.05 

0.5 


1.48 
2.5 



93.9 
0.41 
0.96 
0.68 
1.80 
0.13 




0.53 
3.0 



139 



TABLE 10.— High-temperature properties of optimized and commercial MgO bricks 



Sample 



MOR, psi 



1,300° C 



1,500° C 



Hot load (1,700° C, 
25 psi) deformation, pet 



Slag resistance, vol. loss, In 3 



1,650° C 
BOF slag 



1,600° C, 
glass slag 



B-1 

B-2 

M-1 

S-1 

S-2 

98-pct-MgO commercial refractory 



*360 ±134 
*800±132 
*930 ±133 
"700 ± 25 
*800±205 
120± 20 



*110± 15 
*690±106 
*810±105 
*790±132 
*490±179 
40± 10 




-.03 



+ .92 
+ .89 
-.27 



1.80 
2.11 
2.08 
2.20 
2.00 
1.88 



1.45 
.96 
1.64 
1.55 
1.78 
.94 



•Indicates significant difference compared with 98-pct-MgO commercial refractory at i 
are 95-pct standard deviation intervals.) 



pet confidence level, using t-test. (Figures preceded by 



Results of mineralogical analyses of the optimized 
periclase bricks indicated that periclase was the predomi- 
nant phase in all five materials. The as-received materials 
contained minor amounts of monticellite (CaO • MgO • Si0 2 ) 
and merwinite (3CaO • MgO • 2Si0 2 ). Both samples with addi- 
tions of Zr0 2 (M-1 and B-1) had minor amounts of calcium 
zirconate (CaZr0 3 ) present. This is a refractory phase with a 
melting point of 2,340° C; the original phases of monticellite 
and merwinite have melting points of 1,487° and 1,577° C, 
respectively. All of the optimized periclases, except B-1, in- 
dicated small amounts of dicalcium silicate (2CaO-Si0 2 ), 
with a melting point of 2,130° C. One of the samples (B-1) 
with a 2.0-pct addition of Zr0 2 exhibited a minor amount of 
cubic zirconia. 

IMPROVED MAGNESITE BRICK 

To determine if property improvements might be possi- 
ble in magnesia-based refractories, two commercial 
magnesia refractories (90 and 98 pet MgO) were im- 



pregnated with solutions of 14 different metallic salt and ox- 
ide solutions (10). After impregnation, samples were fired to 
1,550° C to allow salt decomposition and reaction between 
the resulting oxide and the refractory phases present in the 
brick. Subsequently, hot MOR, deformation under load at 
elevated temperature (hot load), thermal spall resistance, 
and slag resistance tests were conducted. XRD was used to 
study the mineral phases that were formed, and energy- 
dispersive spectroscopy (EDS) to determine the distribution 
of the additives. 

Additions of Al, Mg, or Sn to 90-pct-MgO brick resulted 
in statistically significant improvements in hot-MOR, slag 
resistance, and spalling resistance properties. The addition 
of only 1.14 pet Sn0 2 resulted in dramatic improvements of 
hot MOR (200 psi to 450 psi at 1,500° C), slagging resistance 
(1.59 pet area removed to 0.82 pet), and spalling resistance 
(39 pet retained modulus of elasticity (MOE) to 52 pet). The 
high-temperature properties of 90-pct-MgO brick with addi- 
tions of Al, Mg, or Sn salt and oxide solutions are equal to or 
approach those of untreated 98-pct-MgO brick. 



CHROMIUM ADDITIONS TO ALUMINA BRICK 



Relatively few mineral commodities have suitable 
characteristics, such as high melting point, mineral stability, 
and physical and chemical properties, for use in refractory 
materials above 1,000° C. Alumina easily satisfies all of 
these requirements and because of its excellent chemical in- 
ertness finds many applications in very diverse 
temperatures and environments. Impurities associated with 
alumina, including free iron, titania, and alkalies, can have a 
very detrimental effect on the high-temperature properties 
of alumina refractories owing to reactions that produce low- 
melting secondary crystalline phases or glasses, which 
soften at high temperatures, causing deformation and/or 
loss of strength. For this reason, these impurities are avoid- 
ed as much as practical during beneficiation, batching, and 



forming. Small quantities of these impurities are found in all 
but the most expensive refractory products and often limit 
their upper use temperature. Based on the literature from 
several major refractory producers (11-H), impurity levels 
in commercial alumina refractories having A1 2 3 contents 
from 42 to 70 pet range from 1 to 2 pet iron oxide, 1 to 3 pet 
titania, and 0.1 to 2.5 pet alkali. Analyses of refractories 
used in this study are shown in table 11. If small amounts of 
other refractory oxides could be added to react with these 
impurities to form high-temperature solid solutions or 
crystalline phases or to prevent the formation of amor- 
phous, glassy phases at grain boundaries, then the high- 
temperature refractory properties, and thus the upper use 
temperature, could be increased. 



TABLE 11.— Composition and refractory properties of commercial AI 2 Q 3 refractories 



Commercial refractory brick 



B 



Chemical analysis, pet: 

Alumina (AljOj) 

Silica (SiO,) 

Titania (TiCM 

Iron oxide (Fe 2 3 ) 

Lime (CaO) 

Magnesia (MgO) 

Alkalies (Na : + K,0 + Li,0) 

Physical property: 

Bulk density lb/ft 3 . 

Apparent porosity pet . 

Cold crushing strength psi . 

Modulus of rupture (room temperature) psi. 

Hot load test (25 psi to 1,450° C) pet deformation . 



41.9 
53.2 
2.2 
1.0 
0.2 
0.3 
1.2 

144-148 

11.0-14.0 

1,800-3,000 

700-1,000 

1.0-3.0 



58.0 
38.0 
2.4 
1.3 
0.1 
0.1 
0.1 

156-160 

12.0-16.0 

7,000-10,000 

2,300-3,300 

0.1-0.5 



69.2 
26.2 
2.9 
1.3 
0.1 
0.1 
0.2 

157-161 

15.0-19.0 

6,000-9,000 

1,700-2,400 

0.4-1.0 



140 



Thirteen different soluble additives were introduced to 
42-, 58-, and 70-pct-Al 2 O 3 brick (15); however, additions of 
Cr in the form of Cr 2 3 solutions provided the largest im- 
provement to the refractory properties of the brick tested. 
Test specimens consisting of 1- by 1- by 9-in bars and full 
size 9- by 4V2- by 2V2-in straights were soaked in solutions of 
Cr 2 3 , air-dried, and fired to 1,450° C. Mineralogical ex- 
amination revealed that in each case Cr 2 3 • A1 2 3 solid solu- 
tions formed, in addition to mullite and cristobalite present 
in the starting brick. Table 12 summarizes the effects of 
Cr 2 3 additions on the hot MOR, hot-load resistance, and 
slag resistance. 

From table 12 it is noted that Cr 2 3 additions improved 
the hot MOR of each of the A1 2 3 bricks. In the case of the 
58- and 70-pct-Al 2 O 3 refractories, this resulted in a twofold 
to threefold increase. Table 12 shows that Cr 2 3 additions 
also improved the hot-load resistance, although less 
significantly than hot MOR. The most dramatic improve- 
ment was to the slag resistance. In the case of the 58-pct- 
A1 2 3 brick, slag attack was reduced by a factor of 5. This 
results from reduced porosity, increased chemical inertness 
of the Al 2 3 -Cr 2 3 solid solution, and decreased wetting by 



high-Fe slag. These improvements become even more 
significant since they result from additions of only 3 pet 
Cr 2 3 as compared to 10-pct additions typically added in the 
form of chromite to commercial brick. 

TABLE 12.— As-received and chromium-treated brick: average 

values for hot MOR, hot load, and area change following rotary 

slag test 





AI 2 Oj, pet 




42 


58 


70 


Hot MOR: 








Test temperature °C. . 


1,350 


1,400 


1,400 


As-received . . . . psl . . 


530 ± 70 


590±110 


370 ± 50 


Cr 2 3 -treated . . . psi . . 


650 ±100 


*1,610± 40 


*770± 30 


Hot load: 








Test temperature °C. . 


1,680 


1,725 


1,760 


As-reoelved .... psl . . 


4.5 ±0.6 


2.2 ±0.5 


4.1 ±0.3 


Cr 2 3 -treated ... psl . . 


3.6 ±1.0 


2.0 ±0.5 


2.2 ±0.3 


Area change followed rotary 








slag test: 








Test temperature °C. . 


1,500 


1,550 


1,600 


As-received .... pet . . 


11.4±5.0 


10.2±1.6 


11.0±0.8 


Cr 2 3 -treated . . .pet. . 


*4.1±0.9 


*2.2±1.1 


*3.0±0.4 



"Indicates a statistically significant difference based on t-test with 
a 99-pct confidence interval. 



SUMMARY AND CONCLUSIONS 



Research results at the Tuscaloosa Research Center 
during the past 6 yr, related to reducing the quantities of 
imported refractory-grade chromite used in magnesia- 
chromite refractories, can be summarized as follows: 

1. By using a combination of conventional beneficiation 
techniques such as crushing, screening, and dry magnetic 
separation, it was possible to beneficiate waste AOD and 
electric steel furnace magnesia-chromite refractories. Con- 
taminants were liberated by crushing the waste refractory 
to minus 6 mesh, yielding a product having a particle-size 
distribution suitable for recycling into secondary refractory 
products. 

Refractories produced from recycled AOD linings com- 
pared favorably with conventional commercial mag-chrome 
refractories of similar composition. Cold crushing strength, 
MOR up to at least 1,350° C, and slag resistance were ac- 
tually superior for the recycled brick. Firing the brick pro- 
duced from beneficiated AOD refractories to > 1,700° C 
resulted in a direct-bonded brick having improved hot 
strength over brick fired to 1,450° C that had a glassy 
silicate bond phase. 

Refractories produced from recycled electric arc fur- 
nace linings developed cracks during drying resulting from 
the hydration of calcium silicates. 

Copper recovery from waste smelter refractories was 
readily achieved by standard physical beneficiation tech- 
niques. Since grinding to 65 mesh is required to liberate the 
metallic Cu, the beneficiated refractory material will require 
briquetting, calcining, and crushing to prepare a coarse 
refractory grain for reuse in magnesia-chromite refrac- 
tories. Thus, the recycling of the chromite concentrate from 
waste copper smelter refractories is at an economic disad- 
vantage with respect to chromite obtained directly from 



2. The high-temperature MOR and hot-load properties 
of brick produced from optimized periclase grain can be im- 
proved to exceed those for a commercial 98-pct-MgO refrac- 
tory. Improvements in hot strength were attributed both to 
adjustment in the C-S ratio and/or to additions of Zr0 2 or 
Mn0 2 . The optimum additions were found to be different for 
each particular raw material. The hot strength im- 
provements resulted from formation of the refractory 
phases of 2CaO'Si0 2 and CaZr0 3 in place of the lower 
melting silicates, monticellite and merwinite. 

Adding minor amounts of soluble salts of Al, Mg, or Sn 
to an MgO brick results in significant improvements to its 
refractory properties. The high-temperature properties of 
90-pct-MgO brick with these additions equal or approach 
those of 98-pct-MgO brick. 

3. Additions of chrome solutions to 42-, 58-, and 70-pct- 
A1 2 3 brick resulted in general improvement to hot-load 
resistance and very dramatic improvement to the hot MOR 
and slag resistance. Fivefold improvements to the slag 
resistance were noted, owing to decreased porosity, in- 
creased chemical inertness, and decreased wetting of the 
refractory by high-Fe slags. These improvements resulted 
from additions as small as 3 pet. 

Hot-MOR, hot-load, and slag resistance measurements 
on 42- and 58-pct-Al 2 3 brick indicated these properties 
were superior to those of untreated brick with significantly 
higher A1 2 3 contents. Values for 58-pct-Al 2 3 brick im- 
pregnated with Cr were two to five times better than values 
obtained for untreated 70-pct-Al 2 O 3 brick. This could reduce 
the Nation's dependence on imported refractory-grade 
bauxite generally required for high-Al 2 3 brick, as domestic 
alumina resources could be used to produce the improved 
refractories. 



141 



REFERENCES 



1. Morning, J. L. Chromium. BuMines Mineral Yearbook 1976, v. 
1, pp. 297-308. 

2. Johnson, R. E., N. J. Themelis, and G. A. Eltringham. A 
World-Wide Survey of Copper Converting Practice. J. Metals, v. 
31, No. 6, 1979, pp. 28-36. 

3. National Academy of Sciences, Committee on Contingency 
Plans for Chromium Utilization. Contingency Plans for Chromium 
Utilization. Nat. Mater. Advisory Board on Sociotechnical Systems, 
Washington, DC, 1978, 347 pp. 

4. Petty, A. V., Jr. Refractory Properties of Brick Produced 
From Beneficiated Chrome-Containing Furnace Linings. BuMines 
RI 8685, 1982, 16 pp. 

5. Martin, E., and A. V. Petty, Jr. Recycling Spent Chrome 
Refractories From Steelmaking Furnaces. BuMines RI 8489, 1980, 
12 pp. 

6. Cobble, J. R., and L. Y. Sadler III. A Laboratory Test To 
Evaluate the Resistance of Refractories to Molten Slags. BuMines 
RI 8468, 1980, 13 pp. 

7. Pahlman, J. E., C. F. Anderson, and S. E. Khalafalla. Stability 
of Alumina-Base Refractories in Western Lignite-Ash Slag En- 
vironments. BuMines RI 8334, 1979, 16 pp. 



8. Petty, A. V., Jr., and E. Martin. Recycling of Waste 
Magnesite-Chrome Refractories From Copper Smelting Furnaces. 
BuMines RI 8589, 1981, 18 pp. 

9. Bennett, J. P., and T. A. Clancy. Magnesia Refractories Pro- 
duced From Chemically Modified Periclase Grains and Mg(OH)2 
Slurries. BuMines RI 8848, 1984, i4 pp. 

10. Bennett, J. P. High-Temperature Properties of Magnesia- 
Refractory Brick Treated With Oxide and Salt Solutions. BuMines 
RI 8980, 1985, 11 pp. 

11. Harbison- Walker Refractories, Division of Dresser In- 
dustries, Inc. H-W Handbook of Refractory Practice. Pittsburgh, 
PA, 1980, pp. 19-45. 

12. General Refractories Co., U.S. Refractories Division (Pitts- 
burgh, PA). General Sales Catalog, High Alumina Brick and 
Fireclay Brick, 1985. 

13. Kaiser Refractories (Oakland, CA). Product Literature: 
Alumina and Fireclay Brick. 1977. 

14. A. P. Green Refractories Co. (Mexico, MO). Refractory 
Pocket Catalog. 1985, pp. 9-25. 

15. Petty, A. V., Jr. High-Temperature Properties of Alumina 
Refractory Brick Impregnated With Oxide and Salt Solutions. 
BuMines RI 8845, 1984, 18 pp. 



■ U.S. GOVERNMENT PRINTING OFFICE: 1986-605-017/40,097 



INT.-BU.OF MINES,P6H.,PA. 28386 



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